It really depends on the specifics. Copyright laws very from country to country. Using an online international platform like Wikia makes it even more complicated. However, in the US, I believe that copyright is automatically conferred to the originator of the content unless otherwise specified by a written agreement; regardless of whether or not the copyright has been officially registered. However, "content" is a loose term. For example, in your case, does "content" refer to the entirety of the image or the image of the video in your image? That is where the gray area is. If you have made "enough" modifications/alterations or added "enough" new content, you are considered to be the copyright holder for your image. However, if you haven't done "enough", the copyright still belongs to the person who made the video; assuming it was theirs to being with.
The point is no one can really give you a definite answer; even more so since you haven't provided any specifics.
Edit:
Oh yeah. Then there is also the issue of how the copyright interacts with Wikia's licensing.