A first application executes on one or more computing systems to generate a series of original frame pixel data sets for rendering of graphical images associated with the first application execution. A second application executes on one or more computing systems to detect one or more key graphical images present in the series of original frame pixel data sets. Upon detection of the one or more key graphical images, the second application directs replacement of a portion of pixel data in the series of original frame pixel data sets with substitute pixel data so as to generate a series of modified frame pixel data sets for encoding in lieu of the series of original frame pixel data sets.