Web Images:  Images on the web come in a variety of types (aka file formats) suchas BMP, GIF, JPEG, PDF, PNG, PSD, TIFF and many others.  Indeed, there are many other formats available,but most images scanned, downloaded, or taken with a digital camera will be either in JPEG or GIF format. Below, you will find some basic explanations, to explain the difference betweenthe various formats.

BMP or bitmap format is the standard Windows image file format. GIF (.gif): Graphical Interchange Format.GIF is one of the two primary image formats used on the Web (the other is JPEG). GIF files are compressed, meaning that they load faster than uncompressed versions of the same images.JPEG (.jpg): Joint Photographic Experts Group. JPEG, like GIF files, are highly compressed and very common on the Web. JPEG compression is best suited for photographic images.PDF (.pdf): Portable Document Format. Any computer user with the free Adobe Acrobat reader program installed can read -- but not change -- a PDF file. Saving Photoshop projects as PDFs lets you give a read-only copy of the document to anyone. PDFs are most often used to share long documents where preserving formatting is critical, but Photoshop also supports this format for distributing images. PNG (.png): Portable Network Graphics. In the world of Web publishing, this is the new kid on the block. PNG combines the best features of GIF and JPEG, but many Web developers have not embraced it, partially because some older Web browsers do not recognize the format. PSD is the Photoshop native file format. In a Photoshop document we use the .psd format to create or work with images, but we use other formats to publish images in print or to the Web.  TIFF (.tif): Tagged Image File Format. The TIFF format is the most widely used file format in professional print publishing for publications such as newspapers and magazines. Unlike GIFs and JPEGs, TIFFs are not compressed, which means they include all of the data and color information available. That level of quality is a must in reproducing digital images in print and publishing.