I was reading a BitTorrent guide made by J-Kwon and noticed that the size of this simple image was a whopping 171KB: http://img132.imageshack.us/img132/3271/36gz.png Well, I happen to be such a anal person that these type of things annoy me immensely so I ran the image quickly through IrfanView (a great + simple image viewing prog, check it out: http://www.filepedia.com/desktop_software/graphics/irfanview.cfm ) and came up with this: The image has simply been pasted into IrfanView and saved as GIF. The quality is as good as before but now the size is down from 171KB to only ~28KB. It's faster to load and takes up less of your RAM. Remember that some people still rely on modems; If I still were a modem user and realized that the guide thread I'm trying to read was (needlessly) full of 100K+ images I would turn on my heels. Another advantage of the GIF format is that it doesn't smear the text like in this JPG image: In this example the blurring isn't too bad, but if the image had been saved as GIF it would probably look a lot better and possibly also take up less space. Note: If the a image has already been saved as JPG, it's probably of no use to try re-saving it as GIF. GIF compression can't somehow magically correct the smears created by JPG compression and the filesize will probably only get bigger. You can try this though if the JPG in question is of really high quality aka there aren't any visible compression errors. Otherwise forget it. When not to use GIF? In order to the GIF compression work, the image must have a lot of flat color surfaces like for example a screenshot of a wordprocessor window with some text and graphs. GIF cant handle images with uneven colour surfaces (like a photo of someones face for example) very well at all, they will look ugly and be big. In these instances use JPG (set the image quality setting to something like 75 to 80 for web use). Examples of images that GIF compression wouldn't work well with: About PNG: Under right circumstances, using PNG compression can lead to smaller filesize than GIF without any reduction in quality. However, usually it does not. Instead it will lead probably lead to bigger filesize than either GIF or JPG would so I would advice against using it unless you really know what you are doing. About screen captures: Pressing PrtScr will copy the whole screen, pressing Alt+PrtScr will copy only the active window (so you won't necessarily have to crop the image). Moderators: feel free to add this to the "how to post a screenshot or image"-sticky if you think this is good enough.