Pengo, Thank you for your diagnosis; you saved us significant work. Information for others who may find this thread: The problem is not totally consistent. Picture and Fax viewer works normally on my workstation (with administrative access), but JPEGs sent from our Entourage-using department fail everywhere else tested (with no administrative access). Additionally, it seems some JPEGs work and others fail; I don't have enough data for further diagnosis. With one particular JPEG, Windows 2000 could not display it in IE6 SP1+patches or Imaging but could with Microsoft Office Picture Manager 2003 with SP3+patches applied. Other JPEGs fail everywhere. I do not have a suitable explanation as to why this has happened. A process that has been in place for years has suddenly broken. My best theory is that either Microsoft has recently changed their JPEG rendering library or Outlook's attachment behavior. On affected computers, the issue is shared between 2000 and XP and shared, at least, between IE6 SP1, IE 7, Firefox 2, Imaging (2000), Picture and Fax Viewer (XP), and Paint. We did not test behavior with IE8, Firefox 3, or Windows Vista. Since I believe several programs in that list have independent JPEG rendering libraries, it would appear to be a new flaw in Outlook's attachment behavior.