When a company distributes a fansite kit which has official artwork, it normally comes with an explicit agreement and sometimes even has conditions for use, like "corporate web site name, address, and copyright should be visible on all pages where creative work is present" so reusing any of their official art work has a very high risk of violating an agreement. End of story, I doubt you'll ever draw the least bit attention even so.
However, screenshots have been ruled as fair use as you are rendering them on your on equipment and the EULA for software drawing your screen has no exclusion for capturing the output in this case.
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