No, I haven't, because GIFs and JPEGs do not contain executable code. There is no possible way they could be a vector for infection unless A. you were using some kind of malware image-viewer program that deliberately executed some kind of metadata in the EXIF information as if it were code, and you just happened to view specific images that contained a virus payload designed specifically for that viewer, or B. it's actually a VBScript or other executable file named something like picture.jpg.vbs (in which case it's not actually a GIF or JPEG) and you've got extension hiding in Windows turned on so you only see picture.jpg, in which case it's your fault for not turning extension hiding off to prevent exactly that.
I swear, next you're going to tell me that "hackers can turn your computer into a bomb!"
You once again proved to have no clue how this works. Of course there are .gif or .jpg files which are simple scripts or even executables hidden in mail attachments. Those are not ment here.
I talk about manipulated image files, where e.g. some numberic information for decoding is simply wrong and triggers a crash. In such case the guy who manipulated the file planted code inside the image file and uses the "crash", which normaly would happen, to run exactly that data. So, yes. There can be executable data in any media file and it can infect your system, if it is used by the matching version of application, where the bug is still in.
This is exactly what is used to e.g. hack a system using a word document. Or those manipulated PDF files, or even movies where codec errors are used to get control over your system, by letting them crash.
That is why it is important to keep stuff which you frequently feed with data from some external source up to date. If you only create your own PDF or AVI files, that quite ok, but when it comes to surfing, you will get any virus in the world for free, if you just pick the right file download and display it.
There is no need to double click a mail attachment. Even the Playstation2 gets hacked that way. You simply plant a modified DVD Player onto MemoryCard and the console crashes even before the Playstation Logo appears and shows the hacker menu. It does it all the time, because the PS2 does not even have flash memory. It got hacked because the Firmware in ROM has a bug, which gets used to launch own software.
Just visiting the right websites may causes your system to be taken over, because you did no apply the latest fixes for media decoding or the browser itself.
Geit