Photo and signature size for exam forms: how to read the requirements

Exam portals state photo and signature size in pixels, centimetres, DPI and KB all at once. Here is what each number means and how to satisfy all of them.

Almost every Indian exam application asks for a photograph and a signature, states the requirements in a dense paragraph, and then rejects the upload with a message no more helpful than "Invalid file". The requirements are not actually complicated. They are just four different kinds of number written together, and the trick is separating them.

The four things a portal asks for

Format. Nearly always JPEG. Some portals accept PNG for a signature, but JPG is the safe answer and is what most notifications name explicitly. A file that is technically fine can still be refused for being the wrong format.

Pixel dimensions. Written as width by height, for example 200x230. This is exact. A photograph of the right file size but the wrong dimensions is still rejected, and this is the single most common reason an upload fails when the KB looks correct.

File size, in KB. Usually a maximum, sometimes a range. The minimum catches people out, because a clean, well-lit photograph often compresses well below it.

DPI. Occasionally stated, usually as 200 or 300. This one confuses people the most, so it gets its own section below.

When the size is given in centimetres

Some notifications state a physical size — 3.5 cm x 4.5 cm is common — together with a DPI. To turn that into pixels you have to convert to inches first, because DPI means dots per inch:

From inches: pixels = inches x dpi
From centimetres: pixels = cm / 2.54 x dpi
From millimetres: pixels = mm / 25.4 x dpi

So 3.5 cm x 4.5 cm at 200 DPI is 276 x 354 pixels, not 700 x 900. Multiplying centimetres by the DPI is the usual mistake and it produces an image roughly two and a half times too large in each direction.

Worked examples, all at 200 DPI:

3.5 cm x 4.5 cm becomes 276 x 354 pixels
35 mm x 45 mm becomes the same 276 x 354 pixels, because it is the same size
1.5 inch x 2 inch becomes 300 x 400 pixels

If you would rather not do this by hand, paste the instructions into the box on the home page and the settings are worked out for you.

What DPI actually is

DPI is a number recorded inside the file that says how large it should print. It has no effect at all on how the image looks on a screen, and changing it does not change the pixel dimensions or meaningfully change the file size.

This matters because some portals check the DPI tag without looking at the image. A scan can be perfectly detailed and still be refused for being tagged 72 DPI. The fix is to set the pixel size first, then set the tag with Change Image DPI. It is a label, not quality: tagging a blurry scan as 300 DPI does not make it sharper.

Order of operations

Doing these in the wrong order means redoing them, because each step can undo the last.

Crop first. Frame the photograph to head and shoulders, or the signature close to the strokes. Get the composition right before anything else, or resizing will squash it.
Then set pixel dimensions. Exactly what the form asks for.
Then compress to the KB range. Compression changes file size, not dimensions, so this cannot undo step 2.
Then set the DPI tag, if one is required. This changes neither of the above.

Exam Photo Resizer does steps 2 and 3 together, which is usually what you want.

The minimum size problem

A maximum is easy: compress harder until it fits. A minimum is genuinely awkward, because a simple image — a signature on white paper especially — can compress to a few kilobytes no matter what quality you ask for, and there is no honest way to make a small clean picture into a large file by improving it.

The standard solution is padding: extra bytes are added to a part of the JPEG that viewers ignore, so the file reaches the required size while the image stays exactly as it was. Both the exam photo and signature tools here do this automatically when you set a minimum.

Photographing a signature

A signature is usually the harder of the two, because it starts on paper.

Sign on unlined white paper with a black or dark blue pen. A thin pen that skips will still skip after any amount of processing.
Photograph straight down in daylight. A shadow across the page becomes a grey band that whitening cannot fully remove.
Crop close to the strokes. Signature boxes are wide and short, so a signature floating in a large white rectangle ends up tiny.
Sign the way you actually sign. Portals compare this against what you write in the exam hall.

Signature Resizer & Cleaner handles the whitening and darkening, then the sizing.

Before you upload

Check the file against the notification one line at a time: format, then dimensions, then KB, then DPI if mentioned. Most rejected uploads fail on a requirement the person never read, not on one they got wrong.

Questions

How do I convert 3.5 cm x 4.5 cm to pixels?

Divide by 2.54 to get inches, then multiply by the DPI. At 200 DPI that gives 276 x 354 pixels. Multiplying centimetres by the DPI is a common mistake and gives a result about two and a half times too large.

Does changing DPI change my photo quality?

No. DPI is a number stored in the file describing print size. It does not alter the pixels, so it cannot make a blurry scan sharper, but some portals check the tag and reject a file without the value they expect.

Why does the form want a minimum file size?

To discourage heavily compressed, unreadable uploads. It catches people out because a clean photograph often compresses below the minimum, which is why padding the file is the usual answer.

Should I upload JPG or PNG?

JPG unless the notification specifically permits otherwise. It is what most portals name, and some reject anything else even when the image itself is correct.

What order should I do the steps in?

Crop, then set pixel dimensions, then compress to the KB range, then set the DPI tag. Each step in that order leaves the previous ones intact.