If you're going to be replacing the images in the episodes' infoboxes, then you need to overwrite the existing image instead of uploading an entire new one. You can do this by going to the image and selecting "Upload newer version of this file". This may require you to convert your PNG file into JPG.
It's an official game, but it's not a part of the series. That one pic you have in the info box is passable, simply because it's such a drastic improvement over the original, but images from the episodes are necessary instead.
Great job on uploading all the new images though! :)