We have 30,000 pictures on our site. Moz will return 404's on some occasionally, but Google seems to ignore those. Should I 301 redirect all those images when we move to a new site lay-out? Appreciate your views!

For a few days now we are being stalked by a "referrer" site out of Bangladesh, called sky lancers dot net. Their home page is nothing but a login and password. All traffic comes from one invisible inner page. They don't seem to try to login, nor do they use PPC to get to the site. They send thousands of visitors a day. Anyone has any idea what this site is trying to achieve and what their goal may be? All they do is get the bounce rate to skyrocket, the time on the site to go down and the avg page views of course to go down as well, as they click out immediately after they hit the homepage. Any suggestions on what to do about this practice? And what are they trying to achieve? Thanks for your insights guys!