Hi
Using Drag and Drop with jpgs (but see lower down) ...Are you certain that you are releasing the image ON the track concerned. Obviously it will go to a higher track (Track 2) if it is not dragged low enough. e.g. this jpg will go to Track 2...

This jpg will INSERT on Track 1 at the mouse arrow position.....

However as Borate notes...png files and Text clips (images with transparency) will NOT insert and will automatically be placed on a higher track as they are expected to be used as overlays. However, they can be inserted with a second drag downwards to the track concerned.
Nat