Try reading their T's & C's, http://en.wikipedia.org/wiki/Wikipedia:Copyrights & http://en.wikipedia.org/wiki/Wikipedia:Copyrights#Users.27_rights_and_obligations as well as the GNU Licence in general: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License
No, the images are subject to copyright. Generally, unless the image has been been placed in the public domain, you must obtain permission from the owner/copyright holder to use them.
That's correct. If an image is on Wikipedia it doesn't necessarily mean that the image is in the public domain.