I had issues with precomputed alpha when I played with storing data in the alpha channel of images in the browser. In the end, since I didn't really need to 'h

I had issues with precomputed alpha when I played with storing data in the alpha channel of images in the browser. In the end, since I didn't really need to 'hide' the data, I just wrote a few pixels at the top of the image, but even then, I found some services (i.e. gravatar) was modifying the pixel values slightly. I had to just use a bunch of the most significant bits from each pixel. If you're interested why I was playing with all this, it was for storing public keys in gravatar images: http://kybernetikos.github.io/VisualSecrecy/ http://kybernetikos.github.io/VisualSecrecy/