It seems like the only way to get approval for a Bot account is if it adds to or edits information already on Wikimedia. If you try to download any images, without a bot account
If you need between ten and one million files, using Magnus Manske's tools to recurse categories is a good choice. http://tools.wmflabs.org/magnustools/can_i_haz_files.html produces a list of UNIX commands which you can then just run locally.
An alternative, whose interface is in Germany only but easy enough, is https://tools.wmflabs.org/wikilovesdownloads/