[Koha] Images In OpacNav and OpacMainUserBlock

Hello, I'm having a problem inserting some images on OpacNav and OpacMainUserBlock. I tried to insert an image in a simple hmtl tag img. I both tried its relative path as well as its absolute path but they don't show up. I even used the images in the images folder. The text in the alt tag seems to work. Is it really possible to insert images in these sections? Is there another way to insert images in these sections? Thanks!