How to scan a passport size photo using canon printer, scanner cum xerox machine without A4 size?

I always use canon printer, scanner cum xerox machine for scanning anything. But, i have a problem with it is i don't know how to scan only passport size photo without scanning whole A4 size paper.

Answer: 
Unfortunately, my friend, you don't. If it's loaded with A4 sized paper, this is the only size that will come out of the machine.