You can add a border that would result in 10 x 8. There are lots of ways to do it.
The easiest is to just use the crop tool, set it to 10 width and 8 height and drag the box. Then grab the corners and extend them out so that all of the photo is in the box and you have extra at the top and bottom.
If you want to be able to select the color and position of the added border, do this...
Image > Canvas Size
Look at the width and height and calculate what the height would need to be so that the ratio is 10 x 8. For example on the one you posted, the width is 3.75. I wanted to add a little bit of border on the width side also, so I put 0.25 in for the width (with relative checked) and then I calculated that if the width is 4, then 10 is to 8 as 4 is to x. The math is 10x = 8 x 4 = 32, so x = 3.2.
Since the height is now 2.492, I subtract 3.2 - 2.492 and get that I have to put 0.798 on the width. I chose an off white color for the border and clicked ok.
Then I just put some text in the border to give you an idea of what can be done.
I'm sure there is probably a dozen other ways to do this and probably easier, but these are the two that I came up with off the top of my head.
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