<img src="http://gyazo.com/72b43e9aa26e7a97f8e8eba0e7128963.png" border="0" />
Im not sure if it's legal, sometimes big game companies can sue some games and tools have ripped off sprites if they can do.
Space Invader sprite is patented by Taito, it makes me to think what Taito would do... there a lot of space invader sprite in T-Shirt, Cup, Poster, etc. they will not care, but this tool game creator, they may take seriously about this sprite...
8bitrocket.com/2011/08/25/taito-is-going-after-unlicensed-space-invaders-re-makes