Where did the artistic rendering of Jesus originate? There seems to be a pretty recognizable and consistent artistic image of Jesus Christ, despite the lack of evidence of what he looked like. Where did this initial image originate?
Popular Mechanics (of all sources) did a good article on "The Real Face of Jesus".

The article discusses how the current representations of Jesus came to be.  The European image with long wavy brown hair that we're all familiar with in Western cultures isn't universal at all.  Rather, it seems to simply have been an image that artists rendered, and that we, as a culture, find pleasing.  He looks Kind, loving, gentle, and everything we know Jesus was, but it it, of course, just an artist's interpretation, copied and emulated over the years.

From the article: (emphasis mine)


  Further clouding the question of what Jesus looked like is the simple
  fact that nowhere in the New Testament is Jesus described, nor have
  any drawings of him ever been uncovered. There is the additional
  problem of having neither a skeleton nor other bodily remains to probe
  for DNA. In the absence of evidence, our images of Jesus have been
  left to the imagination of artists. The influences of the artists'
  cultures and traditions can be profound, observes Carlos F.
  Cardoza-Orlandi, associate professor of world Christianity at Columbia
  Theological Seminary in Atlanta. "While Western imagery is dominant,
  in other parts of the world he is often shown as black, Arab or
  Hispanic."


Hopefully, the above will do for an answer.  I know it's vague. For a more specific answer, I believe you'd have to find the earliest representation of Jesus that you feel represents the western image we're used to.  This would be a difficult thing to do, and still meet with the site's strong bias toward objective answers (or those based upon commonly accepted canon or a specific doctrine.)  


First, there are thousands, if not hundreds of thousands of artist's depiction of Christ.  Selecting the first one would be like finding a needle in a haystack.  
Second, whether or not an image seems to match the current accepted "look" is a bit subjective.  (Just look at the results here and try to determine which ones do and do not fit.)