Cheat Engine

[Dark Byte]

red boxes only have an ID for the duration of one frame
the next time the screen is drawn each target has a new id

it remembers the position of the previous target that was closest to the screen and assumes that that target will be the closest target next frame as well (for speed calculation)

for more advanced tracking you really have to do some more specific coding (e.g store the stack for each target and use that to get a player id that was drawn)