Google is a reader, period. They are getting better at indexing images but without content your site will not rank well. There needs to be a healthy mix of images and content throughout a site in order to satisfy Google and also your audience. What those ratios of text to keywords are is anyone’s guess. Google doesn’t give out that type of information. However, your content should flow naturally and never look forced to appeal to search engines.

In this webmaster video Google discusses the importance of content on a site.

Does Google still need text to understand my site?