Some good answers for you below, my friend!

Try adding just a regular image. With some themes a plug-in is necessary for a video.

Yes, the training does require some steps to be completed before you move on. You can also put a place holder and move forward coming back to complete it later. Some images are more difficult to get as they are licensed.

You could always use Google search under the 'images' tab, then use the filters to see what's left. Not sure all of them are 100% accurate, in regard to actually being 'free to use and share' but worth a look maybe.