My suggestion is that you compile pictures yourself. You can either take the pictures yourself, or you can gather them from a royalty free website like Morgue File. Another option would be to use the Flickr application, but that may only be of use to you if you are at home. Many school districts block Flickr (including mine).
On another note, I am not for certain how many images you can actually send. I was able to send sixteen when I made this video. That's a pretty nice sized collection for primary elementary students in one email so that the students do not have to go searching through multiple emails.