Image overlay onto the another image

[sykim21]

Hello,
I am trying to show image stimuli(i.e. a big scene image) that are superimposed by another image(i.e. smaller face image) in each trial.
Since I am planning to randomize scene-face pairs, making superimposed images in advance and uploading those images may not be available.

Could you suggest any useful grammar or method for this?

Thanks,