Depending on your program this is what I do:
1) open your word processing program
2) copy the pictures you want
3) paste them on the document
4) adjust the size
5)save photo document as PDF
6) crop photo doc to pics only
7) load to photo sharing site
8) load that pic to signature line
That's how I do it, I hope it works for you. Good luck and let me know if you need help.
Mike