Frame: based on a free metal picture by Rawpixel from unsplash.com
Backgrounds: www.publicdomainpictures.net, Public Domain
Explosion: opengameart.org by GameProgrammingSlave, Public Domain
Extras: www.clker.com (modified), Public Domain
Fonts: SourceSansPro, SIL OFL (see SIL-OFL.txt)
