It's my understanding from the relicensing FAQ that we will be dual licensing GFDL images in addition to text. It seems this will present a unique problem, however, since images and media files are licensed individually by the uploader rather than bulk licensed like Wikipedia text. How would the relicensing of these files actually be accomplished? I can imagine several approaches, none of them easy:

1. Bot Solution - On all File pages on all projects, bot replace all instances of {{Self|GFDL}} (or the project equivalent) with {{Self|GFDL|cc-by-sa}} and add {{Cc-by-sa-3.0}} to all pages which include {{GFDL}} but no CC license templates.

2. Template Modification Solution - On all projects, replace {{GFDL}} with a new notice that includes both GFDL and CC-by-sa. Then rely on volunteers or file owners to eventually remove any duplicate notices due to other license templates included on the pages.

3. Template Replacement Solution - On all projects, replace {{GFDL}} with a redirect to {{Cc-by-sa-3.0}}. (In other words, a clean migration rather than dual licensing.) Then rely on volunteers or file owners to eventually remove any duplicate notices due to other license templates included on the pages. This would also logically entail disallowing GFDL for future media uploads.

4. User Solution - Ask all file owners to dual license their files before August 1st.

Personally, I favor option 3 although it may be the most controversial. Here is my reasoning:

1. The GFDL was never meant for images and is especially ill-suited for them as a free license. If people were actually required to include 5 pages of license text in order to use an image from Wikipedia (like the license says), no one would ever actually reuse images from Wikipedia. Thus it is a free license in name only and does not meet the goals of the WMF or the community.

2. The terms of the GFDL are never actually enforced for images (with a notable exception I'll talk about), thus it weakens the GFDL license and the concept of free licenses in general, since people start assuming they can be routinely ignored. Thus the "wink-and-nod" of GFDL non-enforcement is most pronounced and most problematic for images.

3. The only times the GFDL is actually enforced for images are for professional photographers who use the GFDL as a "back-door" non-commercial non-free license. Many of Wikipedia most well-known photographers (the ones who have dozens of featured pictures) license their images exclusively under the GFDL (often 1.2-only). When those images are then reused by commercial websites, the photographers contact the sites, inform them of the onerous terms of the GFDL and then offer the sites exclusive commercial licenses for a fee. Thus they basically use Wikipedia as a commercial marketing tool for their photographs (in violation of the spirit of the project). This practice is well known among the english Wikipedia photography community.

I've added this issue as an open question to the relicensing FAQ page on meta.