Can two photos be merged, one on top of the other, at a specific location (say at 200,150) programmatically?
No. The program will not allow you to merge two photos at a specific location, one on top of the other. It will only import the images one a background that can be configured by you. Actually, the photos will be separated by a border:
I suggest you try using advanced photo editors like Adobe Photoshop or CorelDRAW.