Secure Download Manager, which downloads either normal EXE/MSI files or encrypted SDC files, and automatically decrypts them, is part of the e-academy License Management System (ELMS) for secure downloads of primarily academic software. This is not to be confused with the similarly named "download managers", employed by warez sites, that are usually malware.
The only app that Yahoo has is YouSendIt (file hosting), that lets you send files up to 2GB via a link you include in your email, which the recipient can download from. None of these are for sending photos in the body of outgoing e-mail.