Google's John Mueller said in a video hangout this morning at the 1 hour, 5 minute mark, that when you link using images, make sure those images at least have some alt text on them. He said this would "to kind of give us the anchor text" for that link.

The question was "Image links versus regular links. Because we, I want us to link to the other websites that we have but showing the logo so it's more user friendly and that people can see it and not only have a text link to that domain name. Would it still be okay to have it the link in the image?"

John Mueller responded "Sure. What I think is is useful there is either that you have the text link as well or at least that you use the alt attribute for the image to kind of give us the anchor text that you want associated with that link."

Google has been telling webmasters to put alt text on images for as long as I can remember but I don't think I ever hear Google say it can act as anchor text, like your'd have for normal hyperlinks.

Here is the video embed:

Forum discussion at Twitter.

Update: Maybe this isn't new, see: