Not too many artists dedicated their sharp eye and creativity to describe and document what Carnival was in their times and since its beginnings.
Although Carnival in Venice started in 1162, I have found no images made in those "ancient" times.
My guesses:
The artists I have found left a strong sign, though, sending an idea of what Carnival represented in those times to whom may be interested to "know a little more".
I chose of course what I found available on the web, or I had in my books, but there isn't much, really. And the documentation I show here is probably the best available, made from XV to XVIII century, basically, when Carnival was at its strongest.
I also used my Photoshop skills in "making the images a little better" but not so much as to falsify them, so I could pass around a good idea of how Carnival in Venice was documented in those ancient times.
The period I have considered is from the XII century when Carnival started, up to the XVIII when it was fading out already, and was then interrupted by Austrian Laws.
I have used images of the XIX century too, which were still be true enough in reproducing situations and atmospheres. Not too many, though.
Almost all the images (prints, paintings) come from artists living in Venice, because they were close to the source, and could feel the vibrancy of the Venice Carnival in first person.
There is more material available, of course, but I think I have used the best - in quality and meaning - to give the best representation possible of the hystorical period.
I hope this will represent a good starting point for your personal research.