This is just an idea and I don't expect everyone to agree.
But I think the formats used here should be limited to *.cdi *.cue\bin *.iso and *.ccd/img (preferably with cue) should be fine aswell.
cdi for Dreamcast selfboot images.
DC patchers recognise cdi's
PSX patchers recognise bin's
Now for my reasoning of this:-
All those formats can be checked over with CD Mage for errors. (Dreamcast self boots can't as CDMage doesn't seem to like the dual sessions for those.)
All those formats can be burned with Free Trial software that doesn't have a certain number of uses or amount of days use.
cue/bin and iso are two of the most common widly acepted formats throughout all PC windows and PC linux systems and burning programs not sure about Mac though.
Mounting CD Images that a user can't burn directly (Trial runs out) then doing a direct copy is not 100% so this is not always a good option. (Still something I recomend trying though if left as the only choice)
CDRWin (free version limits speed) creates cue/bin or iso files, burns cue and iso files
Disc Juggler (free version limits speed and only lets you burn CD's) creates cdi's, burns cdi, cue, iso and nrg files
P.S. Anyone know of any other trialware that does not limit the amount of times/days you can use it?
***Edit***
I'm not saying get rid of the old files but this would be more for future CD Images
I'm not 100% sure about cdd/img's (using cue's) but they seem to be the same format as cue/bin's creating an image of the same game on the same system the bin and img file are identicle in size but I have yet to check that in more detail (I'll have to do that at some point ) there is also something miss leading about the sub files used with ccd's as they get created even when you create a ccd from another iso that does not and can not hold sub data.
sub data is actually something thats used with CD-G's (Karaoke CD's), but I have no evidence that any other type of CD uses sub data, though some say PSX CD's hold that type of data (I can't proove this either way myself but I do know most CD-R drives can't read or burn sub data anyway even though CloneCD apears to).