Can I put a hotspot in a regular image (i.e., not 360 degree)?

The whole point of hotspots is that they don't show, except during development. You can put them anywhere, as they are above other items on the slide. In fact, you can think of every single object on your slide as having its own layer. Moving them up and down on the timeline will make them appear to be behind, or in front of other objects.

As to making them interactive, that is done by creating triggers. Look at the triggers, and you can see the interactions you can give your objects. They come in four parts: Which object you make interactive, what action you want, and when you want it to happen.  The fourth part, which is to set conditions under which it should happen or not happen, is optional.

One further point is that you can create your own interactive spots on the slide. In the first place, almost every trigger can be applied to almost every object. So for instance in your case, if you want something to happen when the learner hovers over, or drags, or clicks on the image, you just attach the trigger to it, If you want the action only when the learner hovers over, or clicks on a specific part of the image, you can do that with a built-in hotspot, or you can create your own spot. Create a shape with no outline, a fill color, and set its transparency to 95%+.