KB, pixels and cm: why forms reject your photo
Most rejected photos fail for one simple reason: the form is asking about one number and the photo was changed to fit a different one. KB, pixels and centimetres measure three separate things, and changing one does not automatically fix the others.
The three numbers
| The form says | What it measures | How to change it |
|---|---|---|
| 20 to 50 KB | File size, how much storage the file takes | Change the compression quality |
| 200 x 230 pixels | The width and height of the image | Crop or resize |
| 3.5 x 4.5 cm | The printed size | Work it out from pixels and DPI |
A phone photo might be 3000 x 4000 pixels and 4 MB, which is far over any form's limit. Shrinking it to 200 x 230 pixels usually fixes both numbers at once. A plain screenshot, on the other hand, can be under the KB limit and still have the wrong pixel size.
Turning cm into pixels
When a form gives centimetres, you need a third number, DPI, which means dots per inch. One inch is 2.54 cm, so:
pixels = cm รท 2.54 x DPI
| Printed size | At 100 DPI | At 200 DPI | At 300 DPI |
|---|---|---|---|
| 3.5 x 4.5 cm | 138 x 177 | 276 x 354 | 413 x 531 |
| 2.5 x 3.5 cm | 98 x 138 | 197 x 276 | 295 x 413 |
| 5.1 x 5.1 cm | 201 x 201 | 402 x 402 | 602 x 602 |
If the form names no DPI, 200 is a sensible starting point, and the pixel limits in the form always come first.
Fixing each kind of rejection
- "File too large": lower the quality a little. Going below about 70% quality starts to show on faces.
- "File too small": this catches people out. A form with a 20 KB minimum will reject a 12 KB file. Raise the quality, or start from a larger crop.
- "Invalid dimensions": the pixels are wrong. Crop to the exact ratio first, then resize, or the face will stretch.
- "Invalid format": most forms want JPG. A file renamed from .png to .jpg is still a PNG inside. Convert it properly.
- Upload succeeds, then the photo looks stretched: the ratio was wrong. 200 x 230 is not the same shape as 3.5 x 4.5 cm.
Check these before you resize
- Follow the latest notification for your exam or job. Limits change between years, so an old list is a risk, including lists on other websites.
- Check whether your photo needs a date or name on it. Some forms require this.
- Look at the background and how recent the photo must be.
- Keep your original. Compressing a file that is already compressed makes it look worse each time.
Signatures are harder
A signature on white paper photographed under a bulb comes out grey. Forms often have smaller limits for signatures, so the grey background wastes the few KB you get. Raise the contrast so the paper becomes pure white, and the file gets smaller and clearer together. The signature resizer does this for you.
Free, no signup, and nothing leaves your device.
Resize my photo