It really depends on all the media (like posters) you upload to the 3rd party sites as well as the permissions associated with it.
If you're uploading copyrighted material that you don't have rights to publish to the web, then its going to be bad referencing that material as your own.
If you upload the material (with the author's permission) to the third party site, make sure you credit the author when linking to the material.
If you upload material, and claim it your own and/or use it in a manner the material's author does not approve of, then you could get sued and/or reported to various companies which could even include the search engines.
So my suggestion is get permission first from the authors of each poster you want to upload before continuing.