Let's assume an image on a tumblr or in a blog post that you made is a form of painting, which many more people will likely see than your actual, physical artwork, unless you hook up with the right gatekeepers and survive 100 other hurdles.
Do you know the first thing about your medium? Duncan Alexander considers some properties of file types that can be read by most internet browsers in his post Let's Be Formal. Possibly you don't need to know any of this, but even if you use straight-from-the-tube paint and prestretched canvas it helps to know a little about the color wheel and different types of surfaces.
What about content? Is your painting automatically kitsch because it's on the internet? A couple of years ago Kevin Zucker discussed some of the "archetypes" buried in digital imaging programs (including "Lena," the Playboy pinup girl Duncan Alexander uses as a model in his post). In a response I wondered whether these "Pottery Barn knickknacks, Playboy foldouts [and] unimaginative nature photograph[s]" weren't still influencing digital expression in some way.
Inherent handicaps aside, the fact that some still question the kitsch factor suggests that the 1960s arguments between abstract expressionism and Pop still live and are currently working themselves out on the Internet.