There's a simple workaround: take your painting to a public place and snap a photo of it.
"Also, it is not an infringement of the copyright in a work if you draw, take a photograph or make a film of, buildings or sculptures or works of artistic craftsmanship which are located in a public places or in premises open to the public and copyright is not infringed in any material when it is used in legal proceedings."
Personally, I think there should be a distinction between unique works (e.g. paintings and sculptures) as opposed to duplicated ones (e.g. prototypes, books, movies, prints, mass produced figurines, etc.) but, as others have pointed out, there doesn't seem to be.