Modding is just a process of combining different resources (Doesn't really matter where it all comes from, unless someone WANTS to be fair to the originals and relatively accurate about the source.) into one coherent package which "feels" like the real thing.
Take something i'm currently working on; X-Com.
I own the games, i can get plenty of alternate material right off the web in numerous places. Everything i plan to integrate into the final X-Worlds mod will absolutely be some strictly exact reproductions of the X-Com series stuff. Say again - EXACTLY like the real thing. As a mark of respect for the excellent art done by previous designers.
Under "the fair-use" rule, most graphics found (even here in already made Mods) elsewhere or in someone's computer are considered valuable assets when developping total conversions. Without it, one would have to redraw and work on "new" material for months even years before a reasonably nice set of files can be assembled. Players wouldn't have access to anything cuz nobody in his right mind would even want to tackle the huge amount of hours... just to pack a Mod which may stay untouched or never d/l by anybody.
See, it's free. It's got no obligations, no purpose other than adding features to a GC installation for anyone to get or not. I'd say it also increases the value of the game, gives replayability factors, suits the need of downloaders when it does.
As for, doubling MODS... i find it quite interesting since competition forces Modders into a sort of quality output mode, pushing the egde ever so slightly that the NEWest version may just be more appealing than what the other guy just did. Consumers win. They always get the best.
Using Copyrighted "things' is another story which i will leave to corporate lawyers to debate. In the meantime, i will not be stopped from gathering whatever is necessary to DO the best X-Com immersion mod that i can. Although, CoSh was denied by an SD-Moderator (and, i really understood why!)... nothing prevents me from redesigning the whole concept and its images to "stay under the radar", while trying to guess what may be alright and re-submit for approval. Caught in a loop, because i truly believe it would be great if GC players could play against SpiderMan, Batman, Gojira, KingKong & Superman, etc!!
There always will be some new kid-in-town whom may just prove us all amateurs when compared to what can be achieved with talent and patience. It takes years to develop skills, just a few minutes to use intelligence wisely; as a result, MODS do get made and roll along the highway of selectable choices. The museum is open, hang up your entry, fakes may fool you - but the creepy stuff still IS there.
Without variety, any game can rapidly get boring enough to simply, abandon it.
Modders do it for FREE, btw.
- Zyxpsilon.