If you apply/secure an E-visa on-line, you will be sent a pdf with the actual Visa.

I recall it includes copy of your passport picture [I threw mine out so can't refer to it for specifics] in the document, the total size equal to a passport page. They merely take that document and then stamp your passport.

The on-line service I used advised to print two copies, and to keep the second copy for when you exit Cambodia. Was not asked to produce it when I flew out; apparently they only checked for the entry stamp in my passport.