The offline strategy (which I haven't started yet) would be marketing the site at dog/cat/pet shows, competitions and meeting.

Online would be maybe sponsoring a few good sites, but mostly relying on the word of mouth of pet enthusiasts that discover the site, and embed thier pets' slideshow into their blog (the slideshow links to their full profile page of course). I'd also like to grow the number of people blogging on pet-files, which would bring new readers, and possibly new writers