Why would you want to reverse engineer them? The whole file format's specifications are available so that anyone may be able to program an image viewer. Even the source code is available (though that costs money). I have both at work, and looking at the main JPEG document, there's nothing in it that could be used to run malicious code. JPEG File Interchange Format features: o Uses JPEG compression o Uses JPEG interchange format compressed image representation o PC or Mac or Unix workstation compatible o Standard color space: one or three components. For three components, YCbCr (CCIR 601-256 levels) o APP0 marker used to specify Units, X pixel density, Y pixel density, thumbnail o APP0 marker also used to specify JFIF extensions o APP0 marker also used to specify application-specific information If you're worried about that last one: "Application-specific APP0 marker segments are identified by a zero terminated string which identifies the applications (not 'JFIF' or 'JFXX'). This string should be an organization name or company trademark. Generic strings such as dog, cat, tree, etc. should not be used." I tell you, it's just not possible, unless you make bogus JPEG files that contain malicious code (which, when opened would appear corrupted) and a viewer program to go along with it that will recognize the instructions and run them (and if you use Photoshop, ACDSee, Paint Shop Pro, etc, it's just not possible as the JPEG instruction set is hard coded). That's the thing with virii (viruses? my French's coming through.. heh), they have to be run. Of course, you can fool anyone into running a virus (naked pics of Anna Kournikova [sp?] seemed to do the trick once), and Outlook Express/Outlook can be configured to run ASP files which could infect you depending on your Internet Explorer settings, but it all comes down to being careful. =DarkPen=