As sharemywin[1] said, you might be able to get a fair number of users; however, the problem would be with monetizing those users. According to [2], you will make very little money with advertisements. (I'm assuming this project is for the money; if not, you can safely ignore this whole post.) I doubt that there would be very many people who would pay for any social network, so it would be difficult to make any money off it.
[1]: https://news.ycombinator.com/item?id=6942207
[2]: http://blog.startupprofessionals.com/2012/03/website-ads-are...
No, really. Facebook is swimming with accounts for peoples' cats and dogs and iguanas and goldfish.
Ditto for Instagram, Twitter, etc. etc. etc. - people use the sites they're already using, and where their friends will see the posts.
At one point, Facebook had catbook and dogbook apps. No idea if they are still there.
As for myself, I'm not a photographer and I don't care to share my personal pictures on the Internet.
The site looks great and there are some great photos there.
But I show my pet pictures to people.
That's the fundamental problem here - the point of Pinterest / Instagram / Facebook is that very few people want to look at one kind of thing, but if they want, they can use search.
There isn't a successful domain-specific search engine; the fundamental nature of Facebook is encyclopedic at this point, similar to a search engine.