here my criteria is to drag 3 images and drop them in 3 different locations. validate before dropping in the location if it already has an image, if yes them pop up an error message. Basically how do I capture drop location ID where the image is dropped? Can someone please help me out urgenlty on this?

ugent help please! here my criteria is to drag 3 images and drop them in 3 different locations. validate before dropping in the location if it already has an image, if yes them pop up a message. Quick response will be highly appreciated. Thanks!