(PHP 4, PHP 5)
imagecolortransparent — Define a color as transparent
Sets the transparent color in the given image .
An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
A color identifier created with imagecolorallocate()
The identifier of the new (or current, if none is specified) transparent color is returned.
Note: Transparency is copied only with imagecopymerge() and true color images, not with imagecopy() or pallete images.
Note: 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.