Anchoring an image over a image in the text box

[Vortilon]

I'm trying to anchor an image on an image which I have put in a text box:



The background image was pasted into the text box so that it moves as I insert or delete text. I then placed the red box on top, but I can't group the two, because the bottom one is strictly "text"; at least that is what I have concluded from the message that appears when I try.

I'm currently anchoring a few characters in from the margin at the start of a sentence, as shown, but I'm not sure this is the best way to do this (sometimes, after text edits, the red box moves off and I haven't worked out why yet).

Can I ask the floor what is the suggested method to achieve both images staying locked together?

Thanks very much for any input.

Cheers, Al