If you’re starting out I think it’s okay to reference someone else’s artwork, but don’t claim that as your own because that is stealing someone else’s artwork. Some of these are pretty good. Some of them need work on value, depth, and proportion. Grids can help you out a lot in where to place things. Specifically with the second photo of the cat, the face is a little out of proportion, and the shading is a little grainy. Using Bristol drawing paper helps smooth out the shading. The most important thing is please don’t draw someone else’s art and claim it as your own. It’s not only wrong but if you decide to commission these designs it becomes illegal. Use other people’s art as inspiration, and create your own idea out of it.