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Hello Gary, You should know that using followable affiliate links is against Google's Webmaster Guidelines, as they are viewed as paid links due to the monetary relationship between merchant and affiliate. With that said, lots of people take the chance anyway and so long as you're aware of the risk... I do think the alt attribute text contained within an image link (as well as the title attribute in the link) is considered by Google's algorithms. It probably would make a very small difference. However, I would not overdo it by stuffing either the file name or the alt text with lots of keywords. Your brand name, or the name of a product or service would probably be OK, but highly-targeted, non-brand alt text in banner ads that link to your site, especially since a lot of banner ads are site-wide placements (i.e. potentially thousands of pages on a single domain) are not a good idea. If it were me I would include a nofollow tag in order to avoid any potential link-based penalties in the future, in which case you needn't worry about alt attributes or filenames beyond making them useful to the visitor.