This spell combines several elements to create a powerful protection from scrying and direct observation. When the spell is cast, the wizard dictates what will and will not be observed in the area of effect. The illusion created must be stated in general terms. Thus, the caster could specify the illusion of him and another playing chess for the duration of the spell, but he could not have the illusionary chess players take a break, make dinner,and then resume their game. He could have a crossroads appear quiet and empty even while an army is actually passing through the area. He could specify that no one be seen (including passing strangers), that his troops be undetected, or even that every fifth man or unit should be visible. Once the conditions are set, they cannot be changed.
Attempts to scry the area automatically detect the image stated by the caster with no saving throw allowed. Sight and sound are appropriate to the illusion created. A band of men standing in a meadow could be concealed as an empty meadow with birds chirping, etc. Direct observation may allow a saving throw (as per a normal illusion), if there is cause to disbelieve what is seen. Certainly onlookers in the area would become suspicious if the column of a marching army disappeared at one point to reappear at another! Even entering the area does not cancel the illusion or necessarily allow a saving throw, assuming the hidden beings take care to stay out of the way of those affected by the illusion.