Here is how I would do it, some work involved but reusable.
Ctrl click one of the photo layers to select it with marching ants, ctrl+c to copy it, ctrl+n for new document, select transparant background colour and click okay, ctrl+v to paste your photo in to the new document.
Make a new layer and click Image/Canvas size, make sure there is a tick in relative and enter a size you want to increase by (a size of 20 in both width and height will increase your canvas size by 10 all round) then ctrl+a to select all and fill it with any colour, then at the bottom of the layers palette choose Stroke from the Add Layer style menu, change the colour to the colour of the border you want and also the thickness, and make sure "inside" is selected, click okay.
Now go to the fill of that layer and move the slider to 0%, so your left with your photo, a transparent area around it and the sharp cornered stroke around that.
Now at the bottom of the layers palette add a new group and put all your layers into that group then drag the whole group into your main document (the one where you want the border).
So now you have your template all you will have to do in the future is ctrl/click the photo layer to select it with marching ants then click "Edit/Paste into" which will paste your new shot in. To resize the newer image to fit this template ctrl+t and then use the grab handles holding the shift key to resize proportionately and your done.
Some work to set up, but easy to reuse again and again.
Hope this helps!
Steve...
