Application portals have a particular way of failing. The upload does not explain what is wrong; it just says no. Then you compress the photo harder, and it says no again, and now the photo also looks terrible.
The limits are not arbitrary, and there are only about four things being checked. Once you know which one you are failing, it takes a couple of minutes.
The short version
- Get the crop and the framing right first. Everything else is easier afterwards.
- Dimensions are checked as often as file size, and are the most common hidden reason for rejection.
- The photo and the signature are different problems and want different treatment.
- Reach a small target by reducing pixels, not by crushing quality.
- JPG. Not HEIC, not PNG unless asked, not WebP.
The four things a portal actually checks
File format. Nearly always JPG. This is the one that catches iPhone users, because photos are frequently HEIC by default and the portal has no idea what that is. Convert before you do anything else.
File size, as a maximum and sometimes a minimum. Photos commonly sit in the 20–50 KB band and signatures lower still. A minimum exists on some systems specifically to stop people uploading a 2 KB blur.
Pixel dimensions, as a range or an exact figure. This is the check people do not know about, and it produces the maddening case where a file is comfortably under the size limit and still refuses to upload.
Aspect ratio. A photograph is expected to be portrait, roughly the shape of a passport photo. A signature is expected to be a wide, short strip. Submit a square and some systems will refuse it and some will stretch it.
What the requirements typically look like
Commonly seen shapes, to give you a sense of the range — not authoritative values for any specific form:
| Photograph | Signature | |
|---|---|---|
| Format | JPG | JPG |
| Typical size cap | 20–50 KB | 10–20 KB |
| Typical minimum | often around 4–10 KB | often around 1–4 KB |
| Shape | portrait, near 3.5 × 4.5 cm | wide strip, roughly 3:1 |
| Background | plain, light or white | plain white paper |
| Content rules | face centred, recent, no hat or dark glasses | in ink, usually black or blue |
Some forms add requirements that catch people out: a photo taken within the last few months, your name and the date printed along the bottom, or a separate thumb impression and handwritten declaration. Read the whole instruction page once before you start — it is faster than discovering these one rejection at a time.
Get the photograph right before you shrink it
Almost everything that goes wrong at this stage goes wrong before any tool is opened.
Take it properly. Plain wall, daylight from the front, no shadow behind you, no hat, no sunglasses, neutral expression, head and upper shoulders filling most of the frame. A photo taken against a bookshelf will not just fail the background rule — the bookshelf is fine detail, and fine detail is what eats your 20 KB.
Crop before resizing. Crop to the required proportions with your face in the right position, and only then reduce the dimensions. Doing it the other way round means you shrink pixels you are about to throw away, then shrink the ones you keep a second time.
Then set the dimensions. If the instructions give a pixel size, use exactly that. If they only give a size in centimetres, a few hundred pixels on the long edge is plenty for something that will be displayed at postage-stamp size.
The signature is a different problem
Treat it as a separate task, because the thing that helps a photograph hurts a signature.
Sign on unlined white paper with a dark pen, larger than you normally would — a big signature scanned down is far cleaner than a small one scanned up.
Photograph or scan it straight on, in even light, then crop tightly to the ink with a small margin. Most failed signature uploads are mostly paper.
Watch for grey speckle. A JPEG of black ink on white develops fuzz around the strokes as it is compressed, and the harder you compress, the worse and sometimes the larger it gets, because noise is expensive to store. If a signature refuses to come down cleanly and the form accepts PNG, try it — flat black on flat white is exactly what PNG is good at, and it will often land under 10 KB while staying perfectly sharp.
If the form insists on JPG, the fix is dimensions again: a smaller, cleaner signature beats a larger, speckled one.
Hitting 20 KB without ruining the face
Twenty kilobytes is genuinely small, and it is where people go wrong by pulling the wrong lever. Crushing the quality setting produces blocky squares across the cheeks and forehead — exactly the part of the image being examined.
The order that works:
- Crop first, so you are not spending bytes on background.
- Strip metadata. A phone photo carries EXIF data and sometimes an embedded thumbnail. On a 20 KB budget that can be a meaningful slice, and removing it costs nothing visually.
- Reduce dimensions until the target is reachable at a decent quality, rather than holding the dimensions and forcing the quality down.
- Check the result at full size, not as a thumbnail.
A plain background does a lot of work here. There is almost nothing to encode, so nearly the whole budget goes to your face — which is the point.
Why it still fails
Working through the usual causes:
- “Invalid format.” The file is HEIC or PNG when JPG was required. Convert.
- “File too large” on a file that is under the limit. Check whether the portal means the photo alone or photo and signature combined, and check whether it is reading the file before or after you cropped it — some upload widgets pick up the original from the file picker.
- “Invalid dimensions.” You met the size limit by shrinking too far and fell under the pixel minimum. Go back up and take the size out of quality instead.
- “File too small.” Same cause, seen from the other side.
- Nothing happens at all. Frequently the filename: spaces, non-Latin
characters, apostrophes and very long names all break older upload handlers.
Rename to something like
photo.jpgand try again. - It uploads but looks wrong in the preview. Aspect ratio. The portal has stretched your image to fit its box.
Before you submit
- Format is JPG, unless you were told otherwise.
- Size is comfortably under the cap, not sitting on it.
- Dimensions are inside the stated range, at both ends.
- The photo is portrait, the signature is a wide strip.
- Opened at full size, the face is clear and the signature has no grey fuzz.
- The filename is short, plain, and has no spaces.
- The preview on the portal looks like your photo, not a stretched version.
None of this is difficult. It is just that the error messages tell you almost nothing, so knowing which of the four checks you are failing is most of the work.