Eventually I may add built-in support for animations but for now you have two ways of doing it:
Update the decal with a new texture each frame.
Put all the texture frames in one texture and animate the uv to point to the correct texture.
Known Limitations
The decal will render from behind as well. (I may fix this at some point)
The decal doesn't actually interact with light, instead it gets the luminosity of the background and does its best to blend in. In practice I haven't had any problems with this yet. If you don't need/want lighting you can turn it off.
Open Source Agenda is not affiliated with "Screen Space Decals" Project. README Source: leopoldek/Screen-Space-Decals