htaccess get content from other folder [closed]

Question

I'm using nextgen gallery plugin in my blog. The default folder for storing images is wp-content/gallery/gallery_name/ . I'm looking for a way to move all images in all galleries to one folder.

Specifically, i want htaccess to rewrite all wp-content/gallery/gallery_name/filename.jpg to something like wp-content/gallery/gallery_name-filename.jpg, that is , to replace the last / to -

I have written the code but it does not work as expected

RewriteEngine On

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^wp-content/gallery/(.*)-(.*)$ /wp-content/gallery/$1/$2 [L]

My question is: what is wrong with the code? How can i correct it?

Thanks!