I may be the only one here but I think the ability to put an image on a casting call would save so much time. Now i realise not everyone is going to want to upload a pic onto there port and PS are'nt going to want that activity on the server but why not allow showing a pic from another host like Flicker. It would be so much easier to explain a shoot with a similar type of image, the amount of times i have had a model cancel a shoot because " she didn't realise what implied nude was" is painful.
there wouldn't be copyright issues if you clearly marked the correct copyright on image or post and you aren't selling the image.
unless you mean by way of copying the image in your work but then i don't mean a direct copy just by way of helping explain a certain look or genre.
For instance rather than explain WW2 pinnup to a model i could show an example.
But I do get that the copyright could be an issue for PS but im sure a cleverly worded set of rules would cover them but then im creating more work for them
Maybe limit it to only using your own images or images already available on Purestorm profiles, would also give people extra exposure that way