So you would have to modify imag[n] for n=1 to nType, and set those to the required filenames (including extension, but without color prefix or directory path).
I used an alert to tell me the value of imag[1] and it said "Pawn.gif". So, I modified imag[1] through imag[6] to have the correct piece names without the prefix or path, as illustrated in my previous comment.
At this point, I have introduced theming. Each button now also changes the colors of the spaces. I've added the Utrecht set, and I tried to change the size by changing the value of sqrSize, but it didn't work. I didn't bother changing squareSize, since it just passes its value to sqrSize.
I used an alert to tell me the value of imag[1] and it said "Pawn.gif". So, I modified imag[1] through imag[6] to have the correct piece names without the prefix or path, as illustrated in my previous comment.
At this point, I have introduced theming. Each button now also changes the colors of the spaces. I've added the Utrecht set, and I tried to change the size by changing the value of sqrSize, but it didn't work. I didn't bother changing squareSize, since it just passes its value to sqrSize.