I have an old site built in 2006, it has around 200 pages and 500 pictures. Every single page is of course indexed as well as images. It is very well ranked for targeted keywords and I receive good amount of SEO traffic (I guess that's due the various campaigns, branding, ppc, etc..)

Problem: Site has outdated design, pages and images have not so proper names, there are no heading and alt tags, it was built in tables, inline CSS etc..

Goal: Complete redisign site, use divs, change file names, add proper meta data, alt tags etc..

Question: How this can affect current SEO positions? I will redirect (301) every single page to the new one, build site map, but what to do with images? Do I need to redirect them also? Any other suggestion?