Pinterest gives out quality image links if you join their platform and post images you use on your website or blog. They get a link from Google every time you post there. Their gain is from the economy they have going with Google.
Some image sites such as Imgur will actually take possession of your image and won’t allow you to gain from it, even if it is clearly a personal picture. They also won’t link you from your image, it is only allowed to post links in the comments section. Those are low quality links. I am avoiding Imgur in the future.