What size is the photo in passport?

Different in different countries. The American one is square, close to 2 inches on each side (but check for the exact size).

In Britain it is 35mm x 45mm.

In all cases the head should be within certain limits, top of head to bottom of chin - sorry, I cannot remember them at the moment.

Much better to check the official government website or passport application form where you are.

It will take you far more time and effort (and possible frustration) if you try to do it yourself; go to any photo department that advertises Passport Photos; they're EXPERIENCED and already equipped and are certain to be accepted by the Passport Office of your country of residence; it WON'T cost much since they're equipped and set up for Passport Photos. Don't complicate your life and risk rejection.

When you apply for a passport it will tell you exactly what size. However it's more than just the size of photograph the distance between the chin and top of the head has to be a specific size. Plus you need a white background with no Shadows. Because of all of these specifics, it would be better if you just went out and had your passport photo taken at a post office or camera store.

This sounds like it is getting at you taking your own passport photo. That rarely, if ever, works. It is more than just an external size. The position of your body in the photo, the light method, the background, and pose all have to meet certain requirements. Taking your own passport photo is a near sure way to be rejected someone along the line. Go to a place that is set up to take a passport photo PROPERLY. Many drug stores, such as Walgreens, do it, and it does NOT cost much. Don't waste time and effort trying to do it yourself. It rarely works.

I suggest you look for this information on your country's passport office web site. A search will take you to the proper page and tell you all you need to know. For the United States, a search term like this will bring up the proper link: "us passport photo" (leave the quotes off).

A UK passport photo must have external dimensions of 35 mm x 45 mm (width x height).