I looked at your MCTEXT1.zip file, and there are a few issues with it:
1) files are in *.png format. The standard format for in-game graphics is *.bmp,
2) those images are way too small to be useable on a major scale. What I mean is, there would have to be a very large amount of objects, to even cover the smallest level size.
Also, I'm actually not sure if copyright would even be an issue with them, since, they all look so general, that it seems like anyone could have made them. Even my 5-year old nephew could have drawn up something so simplistic.