sorry to say, but us crafters rarely ever come across a brand new idea. chances are you aren't the first to want to sell these items.
if i understand you correctly, the type of portraits you do, i've done before in graphic design class. i'm fairly certain that you can't patent or copywrite an art style (take the many "inspired" andy warhol prints of campbell's soup or marilyn monroe. we all gain inspiration from other pieces, so there is a fine line for some people between inspired and copied.
i don't mean to be a bummer though. i'm certain that you make an amazing product, and i do encourage you to plan to create more and even sell. do you have any examples of your creations? perhaps i'm completly wrong interpreting your description.
good luck! the legal stuff is the most confusing and frustrating part of starting a business.