Background Screenshots Becoming Blurry Later

HI everyone.  I'm trying to create a game board in Illustrator with a race track on it.  The track is no problem.  What I want in the background behind and surrounding the track is the actual Google Earth imagery that surrounds the track in real life. I orginally tried a screenshot of the entire area, but that doesn't work since the  game track I created doesn't work with the scale of the real life area around the track.  I then tried taking screenshots of parts of the area and filling them in behind my track in a different layer. This was tedious but worked well. The background maps looked nice and clear. However, I'd save my project and come back later to more on it and I find my background images had blurred some.  Can anyone tell me why they are clear when I'm workign with them and then blur later?  Since I'm taking dozens of screenshots, I delete the orginal screenshots from my computer.  Does this impact the screenshots I'm using in Illustrator?  Do I need to save these screenshots in a certain format to get a better result?  Thank you for your help.