Just noticed this string that appeared in the Gmail search window after I clicked on one of the thumbnails in the "Recent photos" sidebar while looking at a new message from ... let's say email@example.com. It looks like a handy way to find that picture that person sent you that one time.
from:firstname.lastname@example.org filename:(jpg OR jpeg OR png)
Works whether the pictures are attached or embedded in the body of the message, despite what it says here.
You might want to add gif and other extensions, of course.
Note the parentheses, the colons and the absence of a space after them, and the capital ORs. Not positive, but I think those might all be requirements.