Whenever possible, I credit the original sources of my photos and links. If you are not familiar with Tumblr, you may be unaware of the fact that users are allowed to copy the posts of others (called reblogging). For that reason, most layouts are enabled with the ability to not only credit the immediate source of each reblogged post (the person I directly reblogged from), but they also note the original source of the post (the person who posted it to Tumblr in the first place).
You should also know that Tumblr has a very specific search feature, which allows you to search for pictures/posts about a particular subject (for example, shoes). This is how most people find pictures. Just because a picture or a quote is reblogged from a site, it does not mean I follow that particular blog, or know what the majority of the posts on that page are about. I searched for a picture, found one I liked, and reblogged it.
That being said, I am warning you, if you choose to click on the source of each post, you do so at your own risk.