The WebCEO site offers some good tips on Image SEO. Excerpts:

  • If the image constitutes a link, its anchor text is quite powerful in terms of optimization for high image-search rankings.
  • Use high resolution images, if available. Provide different resolutions of images.
  • Check how your image looks in thumbnail size. Stronger contrast is needed to better discern an image, which might lead to more people clicking on and linking to the image.
  • Save photos as .JPG files, and other graphic image types as .GIF. Search engines tend to interpret a GIF image as a standard graphic image with 256 colors, while JPGs as photos with millions of colors.
  • From: WebCEO.com