A recent discussion on the High Rankings forums centered on one search consultant's struggle with doing SEO for a legal site that had about 90% images and very little text. The client was extremely happy with the way the site looked and functioned, and wanted as few structural changes as possible.
Suggestions from the community included consulting with the firm's site design/marketing company to rebuild the site from scratch, replacing specific images with copy and optimizing from there, or leaving the images as is and fully optimizing the alt tags.
The discussion also focused on knowing what you're getting into before you agree to take on a client. Posters questioned whether the search firm would have taken on the job if they'd seen the site -- and whether the contract left room to renegotiate the fees for the unorthodox work.