32-bit BMP? I don't think I've ever seen a BMP use alpha channel. But yes, BMPs are large and shouldn't be used on the internet. Most image hosts have an automatic BMP-to-PNG converter GIF isn't lossy, it's just limited to
256 colors. It also supports transparency and animation, but then again so does PNG and much better. There's very little reason to use GIFs any more PNG is 32-bit, ...