IrfanView is a fast, simple freeware image viewer and editor that supports all major graphic formats, including BMP, DIB, JPEG, GIF, animated GIF, PNG, PCX, multipage TIFF, TGA, and more. In addition, it features drag-and-drop support, directory viewing, TWAIN support, slide shows, batch conversion, and modifications such as color depth, crop, blur, and sharpen.
IrfanView seeks to create unique, new and interesting features, unlike some other graphic viewers, whose whole "creativity" is based on feature cloning, stealing of ideas and whole dialogs from ACDSee and/or IrfanView! (for example: XnView has been stealing/cloning features and whole dialogs from IrfanView, for 10+ years). 
 IrfanView was the first Windows graphic viewer WORLDWIDE with Multiple (animated) GIF support.
 One of the first graphic viewers WORLDWIDE with Multipage TIF support.
 The first graphic viewer WORLDWIDE with Multiple ICO support.

Some IrfanView features: 
 Multi language support
 Thumbnail/preview option
 Paint option - to draw lines, circles, arrows, straighten image etc.
 Toolbar skins option
 Slideshow (save slideshow as EXE/SCR or burn it to CD)
 Show EXIF/IPTC/Comment text in Slideshow/Fullscreen etc.
 Support for Adobe Photoshop Filters
 Fast directory view (moving through directory)
 Batch conversion (with advanced image processing)
 Multipage TIF editing
 File search
 Email option
 Multimedia player
 Print option
 Support for embedded color profiles in JPG/TIF
 Change color depth
 Scan (batch scan) support
 Add overlay text/image (watermark)
 IPTC editing
 Effects (Sharpen, Blur, Adobe 8BF, Filter Factory, Filters Unlimited, etc.)
 Screen Capturing
 Extract icons from EXE/DLL/ICLs
 Lossless JPG rotation
 Unicode support
 Many hotkeys
 Many command line options
 Many PlugIns
 Only one EXE-File, no DLLs, no Shareware messages like "I Agree" or "Evaluation expired"
 No registry changes without user action/permission!
 and much much more