Fonts are not "collections of pictures", though, and haven't been since the mid 1980. Details in http://pomax.github.io/1449777175633/opentype-let-s-learn-ho... but the gist is that a font is a full, complex, 700-page-specced typesetting program that has to be run on a render engine, similar to how a game ROM is run on an emulator or hardware setup. Sure, you need the engine, but there is nothing to generalize: that engine needs to implement a really large spec, most of which is not "drawing a vector image".