It's nothing to do with BT broadband, it's to do with the program or method you use to send your email.
Similarly, how the receiver sees the photo (either embedded in the mail, or as an attachment) depends on the software they are using to read the mail (or how they have it configured)
Personally for anything other than small, occasional photos I'd suggest opening something like a photobucket account (other image hosting sites are available) uploading your photos to there and then just send a link to the photo in the email, then the recipient can choose when (or if) they want to view/download it.