Check the notice, not a page like this one
SSC publishes the required dimensions and file sizes in each examination's notice, and they have differed between examinations and been revised between years. Any figure quoted on a third-party page — including this one — may be out of date for the examination you are applying to.
The notice is the authority. Take the numbers from it, then use this tool to hit them. Applications are rejected for photograph and signature problems in numbers that are entirely avoidable, and almost always because the specification was taken from somewhere other than the notice.