I want to allow users to click "share this" on a page with an image, and then email that image as an attachment I have a site that shows floor plans for houses. I want to allow users to share a floor plan via an email form where they can enter their email address and their friend's email address who they want to share with. Then when they enter their message and submit, the image of the floor plan will be attached to the outbound email from the server.
If you are willing to write your own module, check out the mimemail module. Sending the mail is as easy as this:

mimemail($sender, $recipient, $subject, $body, $plaintext = NULL, $headers = array(), $text = NULL, $attachments = array(), $mailkey = '')


If you store the picture in a imagefield or filefield inside a node, you can put that field into the attachments array and send it.