Not sure with what you want to cover these images with, but beware that it's not allowed to cover your pets with official Neopet images, even just for personal use. Atleast, that is what I found in an editorial:
your pet's look up are you allowed to cover the circle image with your own hand drawn image, that is of your pet's custom design? You're allowed to cover your shields, so I can't see how this could be any different, especially because the pet's name, species, and color are stated above the picture and stats. ~lunatic_kisses
Yes, this is fine, as long as it's used properly. You MAY:*
Cover the image of your Neopet with an image you drew, or were given by a friend with their permission to use.*
You may NOT:*
Cover or alter the stats of your Neopet.
Cover the text or alter the text at the top that states your Neopet's name, species, and colour.
Cover it with the image of a different official Neopet image. (For example, please do not cover the image of your yellow Cybunny with that of a plushie one.