Your photo is the wrong size
Almost always the same story: the photo was made to one country's specification and submitted to another's. There is no single passport photo size, and the differences are large enough that cropping the file you have will usually not rescue it.
There is no standard size
35 by 45 mm is the most widely used format, covering the Schengen area, the UK, Japan's consular practice and much of the rest of the world. It is common enough that people assume it is universal, and then meet an application that wants something else entirely.
- United States: 51 x 51 mm, a square
- India e-Visa: 51 x 51 mm, also a square
- Turkey: 50 x 60 mm, which nothing else uses
- China: 33 x 48 mm, an unusually tall portrait
- Australia: a range, 35 to 40 mm wide by 45 to 50 mm high
- Most of Europe and the UK: 35 x 45 mm
Why cropping does not fix it
Two reasons. Changing the frame changes the ratio, so a rectangle cropped into a square cuts off the sides of your head or leaves the head off centre. And the head measurement moves with it: the specification fixes the head in millimetres, not as a share of the picture, so a head that was correct at 45 mm tall is wrong once the frame becomes 60 mm tall. Turkey is the clearest example, where a normal 32 to 36 mm head fills only about 53 to 60 percent of the frame instead of the 70 to 80 percent people expect.
Check the head height, not just the outline
A photo can be exactly the right size in millimetres and still be refused because the head inside it is wrong. That is the failure that survives cropping, and it is the one to check before assuming a resize will be enough.
The straightforward fix
Reshoot from the original if you have it, or take a new selfie, and generate against the correct specification. Picking the document sets the frame, the head height band and the eye line together, which is the combination that has to be right rather than the outer dimensions alone.
Questions
Is there a standard international passport photo size?
No. ICAO Doc 9303 standardises what the photo must show and how the face is positioned, not the paper size. 35 by 45 mm is the most common, but the US, India, Turkey and China all use something else.
Can I crop a 35x45 mm photo into a US 2x2 inch square?
Rarely with a good result. The ratio is different, so you lose the sides of the head or push it off centre, and the head height band for the US is defined against a square frame.
Why does my head look too big in a Turkish photo?
It probably is. The frame is 60 mm tall rather than 45, so the same 32 to 36 mm head should fill only about 53 to 60 percent of it. Scaling a European crop up to fill the taller frame is a common mistake.
Does Australia really allow a range of sizes?
Yes. 35 to 40 mm wide and 45 to 50 mm high, which is unusual. The head band of 32 to 36 mm is the part that must be exact.