Borders

To create a border You will have to select the image that you like, then click the paint brush tool, choose what size you want and always have it on a soft edge.

Have the opacity always at 100%

Always and only use black and white

For the layers always make a copy of the original layer

once you have painted around the edges with the paint brush tool. go on Filter, Blur, Gaussian Blur.

Once you have done that, this box will appear you can change the pixels to make it more transparent by moving the slide bar at the bottom.

For example

This is the finished project.