- PSD is an Adobe format that should probably be only used to save Photoshop files. Do not distribute PSD files unless you are doing a photoshop tutorial or something. They can be compressed (RLE encoded) but often this compression does not yeild a file that is much smaller. They can contain a lot of Photoshop specific data that the other formats can't, such as paths. - PDF = Portable document format. This is another Adobe format that is good for text documents with embedded graphics. If you are distributing reports or pamphlets, this might be a good format, but don't use it as a "Graphics file format" - TIFF is a flexible format that can use a variety of compression types including JPEG and LZW. Becuase of the fact that it is fairly difficult to write a fully compliant TIFF decoder you may see some programs that will not load certain TIFF files but will load others (there was a patent on LZW until recently and older programs may have left LZW decompression out to avoid paying a royalty). I would not recomend using TIFF because usually JPEG or GIF will suffice, but that's just personal preference. - EPS = encapsulated post script... another Adobe thing. Anything that Adobe provides the file format specification for (http://partners.adobe.com/asn/developer/pdfs/tn/5002.EPSF_Spec.pdf) is likely to be less flexible than formats like JPEG and GIF. Check out the link for in depth detail since this is the format I am least familiar with in your list. - JPEG is a great format for photos. Use JPEG for any photos you have and/or want to submit. All good web browsers support JPEG. JPEG uses a lossy compression algorithm so you will lose some detail when converting other formats like BMP to a JPEG but usually in the case of photos it is not noticable. If you have an illustrated image or a vector image, don't use JPEG because the edges of lines may get blurred. Use a format that uses lossless compression like GIF or PNG (listed bleow) - The main gripe about GIF is that it has a 256 color limit. It has a lossless compression algorithm, but many graphics applications will take out some of an image's detail "behind your back" before saving it as a GIF. If you have an image that has 256 colors or less, or perhaps a grayscale image, GIF is a good format to use because it will not loose any detail. GIFs can have transparency and animation. If you need a format for animated or transparent images on the web, use GIF. - PNG was sort of created to replace GIF since there was a patent on GIF compression. They are good for web graphics but not all browsers support them. They use lossless compression and are not limited to 256 colors. That means any image you take, if you save it as a PNG it will look exactly the same when you reload it. PNGs can have advanced transparency using alpha channels. They have good compression but since they are lossless they often yeild a larger file size for a comparable JPEG image. Use pngs if you need to save something without loosing any detail at all. In short I'd say stick to JPEG, GIF or PNG whenever possible since you have good a good chance that other people will have software to view them. Also, between these 3 you can store any type of image based on what you want... if you want a small file size for a photo: jpeg, if you want an animated web graphic GIF, a lossless representation of an illustrated graphic: PNG, etc.

In my experience TIFF is best used when wishing to save an image for further modification -- as when retouching a photo, or creating digital art -- or simply when wishing to save the most complete high resolution version of a scanned photo or other image. The files will be large, but that's what CD recorders are for. If wishing to upload to the web or send by email, create a copy at lower resolution and/or size in JPG or GIF.