Is there a difference in graphics quality between full screen and windowed mode in casino games?

As far as I can tell from what I have installed/played, the video output for casino games like Poker Video or Blackjack doesn't change between full-screen and "windowed" modes -- the only thing that's different is how much of your monitor is taken up (full-screen, obviously, uses the whole thing).

To be fair, when you move between modes there may be a brief flicker of the screen. I’ve personally noticed a slight graphical corruption when swapping display modes in certain games, but this is merely a redraw artifact and not an indication that one mode is better or worse than another in terms of image quality.

So, if you don't care about bragging rights and just want the most fun gameplay, it's a tossup. Either should give you roughly the equivalent resolution from what I can tell.

That’s right; the pictures don’t vary at all in video poker and other casino games when you are playing in fullscreen mode versus a window. You’ll still see the same graphics; it’s just that you’re viewing them differently. The graphics will be whatever they are, based on what the game designer thought was a good idea, and on what your computer can handle.