Htaccess to rewrite images folder

[eluser]XMadMax[/eluser]
Try this rewriterule:

RewriteRule ^images/([a-fA-F0-9]+)/([a-fA-F0-9]+)/([a-fA-F0-9]+)/([a-fA-F0-9]+)_([a-fA-F0-9]+)\.(jpg|png|gif)$ user_images/$4/$4_$5.$6 [L]

Allow (images) / (3 subdirs in hexa) / (hexa) + _ + (hexa) + . extension