Exam registrations, recruitment portals, passport and ID renewals, university applications: almost every online form asks for a photo and a signature with strict size limits. A typical request looks like this:
| Document | Usual size limit | Usual format |
|---|---|---|
| Passport-style photo | 20 to 50 KB | JPG |
| Signature | 10 to 20 KB | JPG |
| ID card or certificate scan | 100 to 300 KB | JPG or PDF |
A photo taken with a phone weighs about 3 MB. It has to become 50 to 150 times lighter. Here is how to do it in less than a minute.
Step 1: crop before you compress
The smaller the area of the picture, the more detail is left for what matters.
- Photo: keep the head and the top of the shoulders, on a plain light background. Most phones can crop in the gallery app (Edit > Crop).
- Signature: sign in dark ink on white paper, take the photo in good light and crop closely around the signature.
Step 2: compress to the exact size
- Open Reduce image size in KB.
- Select your photo. JPG, PNG and iPhone HEIC photos all work.
- Type the limit in KB.
- Click Reduce image size and download the result.
Or use the page already set for your limit: compress image to 10KB for signatures, 20KB or 50KB for photos, and 100KB for scans.
When the form gives a minimum and a maximum
Some forms say "between 20 KB and 50 KB". If you compress to exactly 20 KB, the file may end up at 19.6 KB and be refused as too small. Type a value close to the maximum, such as 45: the image will be just under 45 KB and respect both limits.
How the tool keeps the photo sharp
The JPEG quality is lowered first, which keeps the width and height of the photo. Only when the limit is very small is the image also made smaller in pixels, step by step, until it fits. You get the highest quality and the largest dimensions possible under your limit, without trying settings one after another.
iPhone photos in HEIC format are converted to JPG automatically, because many forms refuse HEIC.
What if the form asks for exact dimensions in pixels?
Some forms ask for a size in pixels as well, for example 200 × 230 for a photo or 140 × 60 for a signature. Set the dimensions first with Resize image, then compress the result to the size in KB. Small images reach 20 KB easily at high quality.
Checklist before you upload
- The face is centred, well lit and in focus.
- The signature is dark and fully visible, with no shadow.
- The file is JPG (unless the form asks for something else).
- The size shown after download is below the limit.