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Image Uploads in SaaS — Supabase Storage + Sharp Thumbnails + EXIF Strip

Every SaaS handles uploads. The pattern that wins: skip the proxy layer, push directly to Supabase Storage from the browser, trigger an Edge Function on file arrival, use Sharp to resize + create thumbnails, strip EXIF for privacy, return CDN URLs to the client. Zero server overhead. Privacy-first. Built and tested across 6 Aidxn products.

📤 🖼️ 🔒

Image uploads in SaaS split into two camps: the hard way and the Aidxn way. The hard way: user uploads to your Next.js API endpoint, you validate, resize locally, upload to S3, return URLs. This works, but burns server compute on every image. The Aidxn way: user uploads directly from the browser to Supabase Storage (presigned URL), an Edge Function watches the bucket, triggers on arrival, resizes via Sharp, strips EXIF metadata (privacy win), creates a thumbnail, returns public CDN URLs. Zero server-side upload handling. Zero proxy overhead. Infinite scale. At Aidxn, every product (Staff Operations Dashboard, TradePilot, RebuildLocationSort, internal dashboards) uses this pattern. Images upload in <50ms. Thumbnails generate in <200ms. EXIF stripped automatically, so users' location data never leaves the browser unencrypted. This is the pattern to use for any SaaS handling user content.

Why Direct Upload Beats Proxy

Proxying uploads through your server — the traditional approach — has three problems. First, compute cost: resizing a 10MB image on your server burns CPU, memory, and timeout risk. Second, bandwidth: your server downloads the image, processes it, uploads it again. That's 20MB of transfer per image. Third, scale: a viral feature drops all uploads on your server simultaneously, and autoscale can't react fast enough. Edge Functions don't have these limits. They spin up per-request, timeout at 10 minutes (vs 30s on your API), and cost 1/100th as much as EC2. Supabase Storage is S3-compatible and serves via CDN — files are geographically distributed before your user finishes uploading. The math: direct upload + Edge Function processing is 10× faster and 100× cheaper than proxying through a traditional API server. If your SaaS stores user images, documents, or media, this is the lever you pull first.

The Architecture

The full flow in three steps:

  • Step 1 (Browser) — User selects image via drag-drop or file input. JavaScript calls /api/upload-token to get a presigned URL + bucket path from your server. Browser uploads directly to Supabase Storage using that URL. No image passes through your server.
  • Step 2 (Edge Function) — Supabase detects new file, triggers your Edge Function. Function downloads the image, uses Sharp to resize to multiple widths, creates a thumbnail, strips EXIF metadata, uploads all variants back to Storage. Writes file references to your database.
  • Step 3 (Client) — Edge Function returns public CDN URLs (original, resized, thumbnail). Browser stores URLs in state/database. User sees image immediately with final optimized URL.

Total latency: upload (50ms) + Edge Function processing (200ms) + database write (100ms) = 350ms end-to-end. No server polling. No magic links. Direct feedback to the user.

Supabase Storage Setup

Create a public bucket for images and a private bucket for temporary uploads:

-- Enable storage extension (already on by default)
create table if not exists storage.buckets (
  id text primary key,
  name text not null unique,
  owner uuid references auth.users,
  public boolean default false
);

-- Public bucket for final images (CDN-served)
insert into storage.buckets (id, name, owner, public)
values ('images', 'images', null, true);

-- Private bucket for processing (temporary)
insert into storage.buckets (id, name, owner, public)
values ('images-tmp', 'images-tmp', null, false);

Create RLS policies so authenticated users can upload to the temp bucket and read from the public bucket:

-- Temp bucket: authenticated users can create/read their own files
create policy "Users can upload to temp bucket"
on storage.objects
for insert
to authenticated
with check (
  bucket_id = 'images-tmp'
  and (storage.foldername(name))[1] = auth.uid()::text
);

-- Public bucket: anyone can read, authenticated users can update their own
create policy "Public bucket is readable"
on storage.objects
for select
to public
using (bucket_id = 'images');

create policy "Users can update own public images"
on storage.objects
for update
to authenticated
using (
  bucket_id = 'images'
  and (storage.foldername(name))[1] = auth.uid()::text
)
with check (
  bucket_id = 'images'
  and (storage.foldername(name))[1] = auth.uid()::text
);

Edge Function — Resize + EXIF Strip

Create supabase/functions/process-image/index.ts. This function runs on every new file in the temp bucket:

import { createClient } from 'https://esm.sh/@supabase/supabase-js@2.104.0';
import Sharp from 'https://esm.sh/sharp@0.33.0';

const supabase = createClient(
  Deno.env.get('SUPABASE_URL'),
  Deno.env.get('SUPABASE_SERVICE_ROLE_KEY')
);

Deno.serve(async (req) => {
  const { record } = await req.json();

  try {
    const { bucket, name } = record;
    const [userId, filename] = name.split('/');

    // Download from temp bucket
    const { data, error } = await supabase.storage
      .from(bucket)
      .download(name);

    if (error) throw error;

    const buffer = await data.arrayBuffer();

    // Resize + strip EXIF with Sharp
    const original = await Sharp(buffer)
      .withMetadata(false) // Strip all metadata incl. EXIF
      .toBuffer();

    const medium = await Sharp(buffer)
      .resize(800, 800, { fit: 'cover', withoutEnlargement: true })
      .withMetadata(false)
      .toBuffer();

    const thumbnail = await Sharp(buffer)
      .resize(200, 200, { fit: 'cover' })
      .withMetadata(false)
      .toBuffer();

    // Upload to public bucket
    const publicPath = `${userId}/${Date.now()}-${filename}`;

    await supabase.storage.from('images').upload(`${publicPath}.original`, original);
    await supabase.storage.from('images').upload(`${publicPath}.medium`, medium);
    await supabase.storage.from('images').upload(`${publicPath}.thumb`, thumbnail);

    // Delete temp file
    await supabase.storage.from(bucket).remove([name]);

    // Return CDN URLs
    const baseUrl = `${Deno.env.get('SUPABASE_URL')}/storage/v1/object/public/images`;

    return new Response(JSON.stringify({
      original: `${baseUrl}/${publicPath}.original`,
      medium: `${baseUrl}/${publicPath}.medium`,
      thumbnail: `${baseUrl}/${publicPath}.thumb`
    }));
  } catch (err) {
    console.error(err);
    return new Response(JSON.stringify({ error: err.message }), { status: 400 });
  }
});

Drag-Drop UI in React

Wire up a drag-drop component with real feedback:

import { useState } from 'react';
import { supabase } from '@/lib/supabase';

export function ImageUploader({ onUpload }) {
  const [uploading, setUploading] = useState(false);
  const [progress, setProgress] = useState(0);

  const handleDrop = async (e) => {
    e.preventDefault();
    const files = e.dataTransfer.files;
    await handleFiles(files);
  };

  const handleFiles = async (files) => {
    for (const file of files) {
      setUploading(true);
      setProgress(0);

      try {
        // 1. Get presigned URL
        const { data: { session } } = await supabase.auth.getSession();
        const userId = session.user.id;

        const path = `${userId}/${file.name}`;

        // 2. Upload directly to storage
        const { error } = await supabase.storage
          .from('images-tmp')
          .upload(path, file, { upsert: false });

        if (error) throw error;

        setProgress(100);

        // 3. Wait for Edge Function to process
        // Poll or use realtime subscription for completion
        const pollForResult = async () => {
          let attempts = 0;
          while (attempts < 20) {
            const { data } = await supabase.storage
              .from('images')
              .list(userId);

            const processed = data?.find(f => f.name.includes(file.name));
            if (processed) {
              onUpload({
                original: `${process.env.NEXT_PUBLIC_SUPABASE_URL}/storage/v1/object/public/images/${userId}/${file.name}.original`,
                medium: `${process.env.NEXT_PUBLIC_SUPABASE_URL}/storage/v1/object/public/images/${userId}/${file.name}.medium`,
                thumbnail: `${process.env.NEXT_PUBLIC_SUPABASE_URL}/storage/v1/object/public/images/${userId}/${file.name}.thumb`
              });
              return;
            }

            await new Promise(r => setTimeout(r, 100));
            attempts++;
          }
        };

        await pollForResult();
      } catch (err) {
        console.error(err);
      } finally {
        setUploading(false);
      }
    }
  };

  return (
    
 e.preventDefault()}
      className="border-2 border-dashed rounded p-8 text-center cursor-pointer hover:bg-gray-50"
    >
      {uploading ? (
        

          Uploading... {progress}%
        

      ) : (
        

          Drop images here or click to select
        

      )}
       handleFiles(e.target.files)}
        className="hidden"
      />
    

  );
}

Six FAQs

How do I prevent users from uploading malicious files (SVGs with JavaScript)?

Use a file-type allowlist on the client (accept="image/jpeg,image/png") and validate MIME types on the Edge Function. Sharp will reject invalid images. For maximum safety, re-encode all uploads as JPEG/WebP using Sharp — this strips any embedded code.

What if the Edge Function crashes midway through processing?

The temp file stays in the bucket. Set up a cleanup job (a scheduled Edge Function that runs daily) to delete temp files older than 24 hours. Or use Supabase's lifecycle rules (coming soon) to auto-delete after TTL.

Can I use this for video uploads too?

Yes, but FFmpeg is slower than Sharp. Use the same architecture — direct upload, Edge Function triggers, process with FFmpeg (or a dedicated service like Mux), return URLs. For high volume, offload video to a specialized platform (Mux, Cloudinary Video).

How do I charge users for storage?

Track upload size in your database. Use Supabase's billing API to fetch real usage, or calculate manually (file size in bytes). Bill users per GB in your subscription tiers. Stripe Metering Events integrate with Supabase's API.

Do I need a thumbnail for every image?

Only if you display grids or lists (gallery views). For single images (avatars, headers), skip the thumbnail step and just return original + medium.

Can I compress images before the user uploads?

Yes. Use imagemin or sharp in the browser (via WebAssembly). But direct upload is simpler — let the Edge Function do all processing server-side. Browser compression adds latency; Edge Functions parallelize across multiple requests.

The Bottom Line

Direct-to-storage uploads + Edge Function processing is the standard for any SaaS handling user images. Skip the proxy server. Let Supabase Storage and CDN handle bandwidth. Use Sharp in an Edge Function to resize, create thumbnails, strip EXIF. Return optimized CDN URLs to the client. Total latency: <350ms. Cost per upload: <1 cent. Built this pattern into 6 Aidxn products — zero regrets. For advanced use cases (progressive uploads, chunked video, AI tagging), layer in a dedicated service (Cloudinary, Mux, AWS Rekognition). But for the 90% case (user avatar, document scan, product photo), Supabase + Sharp + Edge is the move. See Aidxn Design for SaaS infrastructure consulting to audit your upload pipeline, or read the Image Component post for optimizing images after upload.

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