Tom,
Image search is a bit different - if you are dependant on image search & the names and/or location of the images is changing during migration you have to very careful. (as I am a bit lazy, I just repeat the answer I posted here)
In my experience, the image index is updated much slower than the normal index, and while google is quite fast to index the redirected urls it seems to need much more time for the images. On a previous migration we had the situation where the image thumbnails where still visible in the search results , but as soon you did preview the image the image didn't load as it had moved from it's original location. The problem with image search is that when this happened the position of the image remained in the results but the site behind it changed (at that point we also discovered that an huge number of sites who had stolen our original images).
To avoid this we now migrated the images to the new location and updated the links in the html, but we also kept the same images in the old location until we had the impression that they were no longer indexed.
This strategy seemed to work as unlike the first migration our results from image search were unaffected.
Apart from that, you will have off course have to update the image sitemap as well (if you currently have one)
If you have additional questions, don't hesitate to ask them (I migrated 3 sites over the last year which had 90% of the traffic coming from image search)
rgds
Dirk