These trojan horses are mostly confined to a few inappropriate sites and are poorly written, but a real JPEG email virus could be just around around the corner. Please get patched up on Windows/Office and make sure your AV protection is up-to-date

MS04-028 - Trojan.Moo: First Trojan Horse emerges
http://secunia.com/virus_information/12353/moo/
http://www.sarc.com/avcenter/venc/data/trojan.moo.html

Trojan.Moo is a Trojan horse program that exploits the Microsoft GDI+ Library JPEG Segment Length Integer Underflow vulnerability (described in the Microsoft Security Bulletin MS04-028).

Note: The latest McAfee DAT files will detect infected files created by Hacktool.JPEGDownload.

Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows XP

Backdoor.Roxe
http://www.sarc.com/avcenter/venc/data/backdoor.roxe.html

Backdoor.Roxe is a backdoor Trojan horse program that exploits the Microsoft GDI+ Library JPEG Segment Length Integer Underflow Vulnerability (described in the Microsoft Security Bulletin MS04-028).

Note: Virus definitions released September 15, 2004 and later detect this threat as Bloodhound.Exploit.13.