Instead of saying true art you could say fine art. There is a difference between fine art and illustration.                                       
 A Generalized short list:

• Illustration often uses lines to define surfaces while fine art generally uses ahding to do the same.
• Illustration is generally figurative , fine art, well not so much
• illustration generally tells, or fills out, or accompanies, a story where in fine art there is no such requirement
  -Sci-Fi is generally thrown in with illustration although I have seen some great abstracted sci fi pieces that could only be considered fine art
• The difference may also be garnered from where the piece of art resides or is supposed to call home. If it adorns the pages of a magazine or a book and if it was created within an agency who was hired to create it then it is probably illustration. if its telos is to hang in a callery or decorate a persons wall then it is probably considered fine art. I think that Frank Frazettas book covers are illustration but when that original oil bookcover is framed and hung in a gallery then I would personally consider it fine art..

One mans opinion with a little factual resonance...