They said a picture worth a thousand words, but this is not true for WebPages and SEO. As it is very clear for me and you to see what is inside an image, it is very hard for search engine to see it, for the search engine an image is a file name. this post should help you how to give the search engine more information about images so images WebPages indexed much better.
There are many ways that you can go to maximize the ability of a search engine to get important data for indexing your pages properly.

Put the keyword in text that surrounds the image.
By putting keywords relative to the image subject in the text around the image can benefit also.

Words rescue.
Try to rescue the text which is inside the image or flash, you may need the “noscript” tag for this. This way the text in the images is placed as a normal text on the page

Put an image caption.
By putting an image caption with the right keyword help the search engine to understand what the image show.

Put Keywords in the file name of the image.
it is very helpful to name the image with a keyword relative to the image content, this way help the search engine to understand the idea of the image also to index the image in the right keyword

The Use of Alt tags
by using Alt tags is important. It seems that Alt tags are used by search engines for a better understanding of the WebPages.

Uses Keywords in anchor text.Anchor text or link text in the url help also index the pages that have a lot of images.