"Invalid image dimensions" — the upload error that has nothing to do with file size
This error is about width and height in pixels, not KB. Compressing the file again will never fix it. Here is what the portal is checking and how to satisfy it.
This is the single most misread error on Indian exam portals. It says nothing about file size, yet almost everyone who sees it responds by compressing the photo again — which changes the KB and leaves the dimensions exactly where they were.
What the portal is measuring
Every image has a width and a height counted in pixels, separately from how many kilobytes it occupies. A 3000 x 4000 photograph and a 200 x 230 photograph can both be 40 KB. The portal reads the two pixel numbers out of the file and compares them to what the notification specified. If either is wrong, you get this message, and the file size is irrelevant to it.
Find your current dimensions
On Android, open the photo in Google Photos and swipe up, or tap the information icon — the dimensions appear as two numbers separated by a multiplication sign. On iPhone, open the photo in the Photos app and swipe up. On Windows, right-click the file, choose Properties and open the Details tab. On a Mac, select the file and press Command-I.
Set them exactly
Exactly is the word. A portal that wants 200 x 230 rejects 200 x 231. Open the exam photo resizer, type the two numbers the notification gives, and drag the picture inside the frame until your face sits where you want it. The output is those exact dimensions, not approximately those dimensions.
When the notification gives centimetres instead
Many notifications specify 3.5 cm x 4.5 cm and leave you to work out the pixels. DPI means dots per inch, so centimetres have to be converted to inches first:
pixels = centimetres ÷ 2.54 × DPI
At 200 DPI, 3.5 cm x 4.5 cm is 276 x 354 pixels. The common mistake is multiplying the centimetres by the DPI directly, which gives 700 x 900 — an image about two and a half times too large in each direction. If the notification names a DPI, use it; if it does not, 200 DPI is the usual assumption for exam uploads.
If you set the dimensions and it still fails
Check the format next. A PNG renamed to .jpg keeps its PNG header, and a portal reading the actual bytes refuses it. Drop the file into the rejection checker, which reads the format from the file itself rather than from the filename and tells you what it really is.
Questions
Does compressing the file change its dimensions?
No. Compression changes how many kilobytes the file takes, not how many pixels wide and tall the picture is. These are two separate things and portals check them separately.
My photo is 200 x 231 and the form wants 200 x 230. Will that pass?
Usually not. Dimension checks on these portals are normally exact comparisons, so one pixel is enough to fail.
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 is 276 x 354 pixels. Multiplying centimetres by DPI is the usual error and gives a figure about 2.5 times too large.
Can cropping fix this?
Cropping changes the dimensions, so it can — but only if you land on the exact numbers. Setting the size directly is more reliable than cropping until the numbers happen to match.