Memory Alpha doesn’t want people linking their images on external sites (which costs them bandwidth without getting any traffic), so they refuse to render images linked on another site. It’s not a legal or moral problem to link these images, they just won’t work.
For an example of what this looks like, go to Commander Shelby’s page and check out the image of her in TNG. If by some chance you were the person who added that image, either clear your browser cache or go to the page in a different browser to see the problem.