Images having a transparent background can be easily stacked ... but once you release the mouse button, the outline disappears. Once the selection is complete, right-click on the selection area.

Here's a clever tool that lets you see through open windows and folders just using your mouse's scroll wheel. Using the second technique, you can quickly make a window transparent, reference ...

N.B.: The last option only works if you have another image open or if you are using a blank Paint file. In either case you will find that your figure now has a transparent background and that you can ...