Perhaps I'm reading this wrong but it seems your Canon is capable depending how old it is but the photos you are getting off google are low res. When you blow up the low res google dirt track to insert the high res car, the dirt track becomes blocky.
If this is the case then your problem is googles low res photos.
what size do you want to enlarge it at?
On Google Images it asks if you want larger photo and gives you the choice of lots of resolutions but when you pick a resolution it still turns out the same.