gingey.j says:

tattooing over scar tissue can be quite painful for you and quite difficult for the artist. however, depending on the design and artist you choose, you can definitely better your chances of getting a tattoo which will successfully mask your scar and won’t cause you too much pain. for example, a design which allows the simplest of color, outlining and design to go right on top of your scar will enable the artist to go over your most sensitive tissue quickly and easily, without creating too much distortion. you can still get a very intricate and colorful tattoo to mask your scar–provided, as i’ve just mentionnned, that simple shading or very few outlines cover it–.
i recommend you look around for reputable shops with artists known for cover-up tattoos; looking through various portfolios will give you an idea of what an artist is capable of, and it may even give you a few ideas for the kind of design/color you’d like. i strongly recommend you discuss your options with the artist of your choice and have him/her make several designs/stencils (if need be) before you finally settle.