How to recognize a 'real' .iso...?
That is the problem, you can't.
Every .iso file consists on one large block of data, it has no TOC, no fs, no nothing, just the pure data track.
Using an audio cd for .iso will make it "easy" to provide said TOC (the .cue file), because every pure audio cd consists of audio tracks only, some have more, some have less. (Dont get me started on data discs)
In my case, the "single" consisted of three tracks.
If i hex edit this .iso i can see a lot of blank space at the beginning, the next .iso from a "longplay" cd starts with data right at the first bit.
Every .iso is different and so far i have not found any marker to make it distinguishable (e.g. with DefIcons)
There is, as far as i know, no program on the amiga who can produce .iso files (there are some on aminet, but none of them worked under OS4)
So, either you split up whatever you are trying to achieve (let's say backup your cds as .iso under Linux and use them under amigaos) or you code yourself a "RAW/AIFF/AUDIO CD to .iso" imager
...eh, and what Niels said...