It really depends on where the email goes, I think. You need to be able to connect to the email system and find the email that is sent by the camera. Then, you need to parse the email to grab the image, and save that image into a directory on your server. Of course, you'll need to have a viewer page that can grab any file that shows up in that directory and show it.
To get you started on accessing your email via PHP, I recommend going here. That should get you started down the right path.
