Hi
Has anyone any suggestions for removing stains/discolouring on an image (see attached).
Ben

Well you need to use layer masks. To start I would recommend you use a curves adjustment layer and use screen blending mode. Fill the mask with black and fill in the dark areas of the photograph by painting the mask with a soft white brush at about 50% opacity.

Then you can use the curves to lighten up the result to "about right." Then combine the correction to a new layer by selecting merge visible layers while holding the option/alt key. This places a combined layer at the top.

Place a new layer above this and use overlay for the blending mode. Then using the default black and white colors and a 50% soft brush paint in black to darken or white to lighten.

Thats one way.

Mmm.. I see where were going on this but "...combine the correction to a new layer by selecting merge visible layers while holding the option/alt key" doesn't work! The Layers menu closes if I hold the Alt key

Well I've enclosed the first step. Using and curves adjustment layer with screen blending and a mask.

More work needs to be done so to "stamp all visible layers" puts the combined info on the top and then with a new layer you can adjust the smudges with overlay blending mode and painting with a soft black or white brush.

Thanks Phil. Once again I've learnt new techniques and got a similar result as the one you kindly posted.
I still don't understand this use of the Alt key when using Layers/Merge visible.
I assume it's the same as making only the adjustment Layers visible then using Select all - Copy Merged - Paste.
Thanks for your help

Hold down the alt key, left click and hold down the mouse button this will keep the menu open. then just move down to merge visible to stamp to a new layer.

I used levels adjustment with a lot of masking. I’ve also enhanced details with dodge & burn tools.