Images don't support alpha channel, only textures do. You may use one of the sprite libraries that are using sprites to emulate images, using the 3D Chip and therefor allow a lot of fancy stuff like blending modes, alpha transparency, scaling, rotation etc. with the speed of light.
There are some ready to use free solutions, right now I cannot find the links.
There are some ready to use free solutions, right now I cannot find the links.