This read only variable returns the height of the sprite
that has been assigned to the instance. This height is returned in
pixels and will be dependant on the image_yscale. If you need the
un-scaled height you should use sprite_get_height.
if sprite_height !=
image_yscale = 1;
The above code checks the height of the sprite assigned to the instance running the code against the height of the sprite resource and if it is not the same, it resets the image_yscale to 1,