Second: Why don't people credit properly on it? :(
Recently, I came across the following: Dear Pinterest, an article by Link With Love (which I support). I think too you should link as much as you can to the original post. Sometimes it's impossible though so deleting all pins not linking to original sources is maybe a bit too much. Linking to the original source is not entirely nessecary at all times in my opinion (e.g. in case of Flash websites), as long as it's linked to a website that links and credits the original maker.
I posted below here some guidelines I follow when using Pinterest and how you can pin things on your Pinterest board with respect for the makers. Because making a living as an artist is pretty rough and we honestly can use all the credits we can get. So please do. :)
I've been using Pinterest for quite a while now and I learned these things below by trial and error. I made these mistakes too but I'm trying to do it correctly with new pins.
Using Pinterest more and more I found out how you can use it without harming artists/makers. These are just my own personal guidelines. I hope you find them useful but they're not official of course. :)
If you see something on a blog or the web you love and you think: "I MUST pin this!", please check if the maker of the image has a website of their own. Pinning the image directly from the maker's website or blog is much better for the maker.
If you find something nice on, for example, an inspiration blog, please check if the maker is credited on the blog and if there's a link to their website. If that's not the case it's a good idea to look up the maker yourself and properly credit.
If you know who made it there's no reason not to credit them. You can also try finding out yourself. Sometimes I use TinEye, quite a handy tool!
If you really can't find the name, ask others by writing something like "maker unknown, does anybody know?". Easy-peasy!
It's so much better when pins are linking directly to the correct blogpost/website page/etc. I come across so many pins that are attached to the home of a blog. You will NEVER be able to find the name of the maker this way. Or you have to go searching through hunderds of posts.
If you're pinning something from a blog that's in a specific post, go directly to that blogpost by looking for the permalink. In most cases you can find the permalink by clicking on the title of the blogpost. When you're at the actual page of the blogpost, you can pin the image to your Pinterest board.
If you repin something, check if the original pinner has credited the maker and if the image is linked to a website with credits. Sometimes I find images that don't lead to anywhere. Big fail.
Of course it might not be possible to do these things always but it really helps if you properly credit and link as much as you can.