According to Thomas Boutell's (author of the C-based GD library to which Lincoln Stein has provided the Perl interface) documentation, CopyResized() is indeed a void function, as are the other copying and resizing functions:

void gdImageCopyResized(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int dstW, int dstH, int srcW, int srcH)

If you're having trouble with GD and can't find an answer in Lincoln's pod, look at Boutell's documentation. If you're still stumped, there's always the source...

-- grummerX