Thanks for the feedback, everyone, all much appreciated!
I am the last person who should be giving out any tips, I am really new at this myself! Anyhow, I’m sure there are much better ways to get the result, but basically these were done by just merging the two images. I took the shots of the people, and found some broken bits of wall I thought were interesting. I traced (lasso tool) the people and pasted the cut-out onto the wall pic, then just played with the opacity (is that a word?) until I liked the “mix”. Then I rubbed out (eraser tool) the bits where I thought the background should show through completely. I was trying to achieve a sort of mural effect – as if the portrait has originally been painted onto the wall and had aged with it. It didn’t look too convincing, so I added a shadow to the pasted pic of the person which seemed to make it look better. I’m sure there was a much more technical way of explaining all that, I’m not really up on the terminology!

Pepsieileen, the people hated their portraits (too spooky – I was not thinking about how much the spirit world is part of the culture, anyone you can see through is a ghost, so in effect these were pictures of them dead – oops!) Next time they get the plain shot.

As well as playing with opacity, try playing with the blending options. There are options like hard light, screen, multiply, overlay etc, which can give you some really good effects.