Ok, this tip comes after I have been noticing many people using the ".gif" format for their photographs they post to the internet. What is wrong with using ".gif" format? Absolutely nothing... if you are posting art without many gradients such as logos and etc. or if you are creating an avatar for your favorite forum or just need a quick and simple animated graphic. If you are using ".gif" format for your photos that are posted to the net... you should be slapped though. Seriously.... a good whack to your head is called for. Let me explain why.
Many people are not aware of the limitations of the ".gif" format and what its purpose is. First, GIF stands for Graphics Interchange Format introduced by CompuServe in 1987. GIF supports 8 bits per pixel or up to 256 different colors from the 24-bit RGB color space. Since GIF's only offer 256 colors out of the thousands we normally see in a photograph or images with continuous color found in gradients, it is not best suited for use for photos due to these color limits. It works better for simpler images with less color needs like graphics or logos with solid areas of color.
Now we come back the ".jpg" format known as JPEG which stands for Joint Photographic Experts Group. JPEG (or JPG as is commonly seen in use) will allow much more color information to be retained than the GIF variation. This alone is a good reason to use it for photos for better image quality than GIF. There is another reason its better for photos on the internet too. It compresses the file and decreases file size for faster delivery. The compression can be adjusted on the author end allowing lots of compression for smallest files and lower image quality or less compression for better image quality. This makes JPEG the most common format for images delivered on the internet.
I have made an example of the same image that was saved as a 256 color GIF file and also as a 3/4 compressed JPEG to show the differences. To some, the difference in appearance at 100% may not be real apparent without a good eye for detail so I blew both up to 200% and cropped it to an area most affected. The JPEG file was smaller at 104kb and the GIF file larger at 160kb. This is something else to consider even if you feel GIF does well enough for your photos. The GIF file is normally larger and will take longer to download or display on the web page besides having a nasty grain look in the photo and lack of detail. See examples below. The GIF version is on the left. Click to enlarge and see the poor quality. The JPEG version is on the right. Click to enlarge and see how its less grainy and better detail overall.