I have been concerned by the quality and authenticity of many supposed portable rock art finds sprawled over the internet. Although analyzing and describing these stones can be very difficult, on the whole the stones should speak for themselves, and any genuine piece should have glyph content all over it. In some places I have seen some obscure rocks that bare little resemblance to there descriptions and scribblings over the photos, which only adds more doubt to the stones authenticity. (if a picture needs to be drawn, the rock is obviously deficient, and would not serve the supposed intended purpose.)
Interpretations of animals and hominids is another grey area, we can never be certain of what we are looking at, even if it looks like a human, it certainly does not mean it is, and nobody can ever prove it. Apart from finding these things in sit tu, our only clues about the date of these artifacts is the species, and these can be hard to interpret, most of all when dealing with humans, apes and hominins. So again it is better to be vague in these areas and let the images on the stones speak for themselves.
Continuity in finds should also be of concern, finds should be comparable across collections, materials should be the same, if not similar, obvious working marks should be present, important subjects like elephants should be repeated throughout the assemblage with other repeatable glyphs present too, when dealing with them as a collection, which of coarse is the only way to shed any real light on them.
A word on Religion, shamanism, and deep space alien’s in old paleolithic times, when on the subject of portable rock art, these are just fantasies of the mind and nobody has one shred of evidence to support these kinds of claims, apart from a few not so old 'Venus figurines' there is absolutely nothing to learn about religious or shamanistic practices, so why even bother? There is a little to learn about cultural traditions in the artifacts themselves, but this will tell us very little of the people themselves. What these objects undoubtedly are is tools, communication tools more specifically, which is hard to take on board at first, until you consider that at some point in our history people were unable to verbally communicate with much meaning. If your suspected portable rock art has no use in this way as a tool, then forget it, its a rock and probably nothing more.
But on the whole I would say that the majority of finds presented to myself by collectors are most likely genuine artifacts, and many people are furthering the study and do know whats going on here, Thanks in this department go to Bruce Cox, Roger Pascal, Dennis Moore, Ursel Beneckendorff , Keith Stamper, Charles Belart and Athena Cumpton.