Popisint imagecolortransparent ( resource image [, int color] )
Sets the transparent color in the given
The identifier of the new (or current, if none is specified) transparent color is returned.
Poznámka: The transparent color is a property of the image, transparency is not a property of the color. Once you have set a color to be the transparent color, any regions of the image in that color that were drawn previously will be transparent.