Not sure if this is any use, but it's very interesting that you can calculate the size and bounding box of a sprite's costume by exploiting the fact that scratch will not move a sprite offscreen, but will always leave it 15 pixels away from the edge. Using this fact we can attempt to shift the sprite offscreen to the bottom left, then top right and use the actual positions achieved to calculate its size and the position of the offset center. When you rotate the sprite you can see it's bounding box changing. It may look like the box is getting too large on some costumes, but this is because all sprites are actual rectangular, so the invisible corners of the rectangular costume extend out further than the sprite when it is rotated. If you look inside, there are also custom blocks to allow us to size a sprite to a specific width or height in pixels!
