Can You Own the Content That's on Your Tumblr Blog Page?by Aaron Parson
Social media, content hosting and blogging websites use a variety of legal techniques that allow them to publicly display your content. Tumblr does not directly claim ownership over the material you post on your blog, meaning you can freely use it again elsewhere. Though you retain ownership, Tumblr does have the right to reuse or modify content you post without further permission.
Posting your own creations to Tumblr -- such as your own writing, photos or music -- does not forfeit your intellectual property rights. Anything you owned prior to posting you will still own afterwards. This also applies to customizations made to your blog's theme and any other behind-the-scenes coding.
Posting material on your Tumblr blog grants Tumblr a non-exclusive license to use your material without paying royalties. Tumblr needs this permission in order to host your posts on its servers and allow other users to see and reblog them. If you'd rather not have a particular post potentially reblogged or modified by other users, you should mark it as private.