What's the best way to make a photo the backdrop/mask?

What's the best way to make a photo the backdrop, behind the original video foot?

I have video footage of someone singing in front of a plain wall (beige pastel color wall). I now want to add a photo as the backdrop. I was able to insert the photo on it's own "video" track, and made it the "mask multiply" (I think that's the right wording), and set my "video" footage/track as the "default", etc.

In "preview/playback" I "am" able to see the photo merged with the original video (looks like it's overlaid/transparent, which is what I want), but the transparent photo is in the foreground, not the background/as a backdrop. When my subject moves around their body/face gets hidden/is partly covered by darker parts of the photo... I tried adjusting the level/amount of transparency on the photo track and on the original video footage track, but that only makes the "whole" footage darker.

Should I have stretched the photo across the whole time line, timed it out as I want it, then saved the photo footage, then stated a new project using the photo footage as my original, then added my singer's footage as the mask (i.e. reversing the process)?

What's the best way to make a photo the backdrop, behind the original video footage (and I do not have to keep the original backdrop/beige color wall as the backdrop; meaning, the photo can be a solid backdrop, not a transparency).

Thanks in advance.