"a certain picture is present on my screen" - By this what do you mean (specifically) e.g. if it's open in an editor/viewer? Do you want it recognised by the image itself or the name of it? (name can be done[image can too but would take loads of programming to do])...
could you give an example of why you need this functionality? (this will help in showing what you want done)...
As the others have said, we need to know which of those options you want, and also in what program you are writing, as methods vary widly, but i can provide for a few if needed!
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