lucy24 - 7:54 am on Jul 4, 2012 (gmt 0)
Do you have a doodad that will automatically shove all new uploads into the appropriate directory? If you don't change the physical file structure, you still have a directory containing 1,5 lakhs of files; no combination of Rewrites and Redirects will change that.
Are the image files directly accessible by name, as in image-hosting sites, or can they only be called by pages? If they're not human-accessible, there's no need for a Rewrite. html pages don't know from pretty URLs.