How to archive blurred edges

We can select just the area we want to blur in a layer, so this is maybe a different way of coming at it.

I used the Object Selection tool using its 'People' function to select the man.

I made a temporary layer and filled that selection with black just as a way to save the selection.

I selected the main layer and hit the Q key to turn on Quick Mask.

Ctrl clicked the temporary layer to load the selection and used Edit > Stroke which gave me the situation below.

Turn off Quick Mask which leaves the thin band selected, and use Gaussian blur

I should probably have removed that area across the bottom of the image before blurring, but you get the idea.

You would also very likely not want the edge of the blurred area to be sharp like that, so use Shift F6 to feather the selection before applying the blur

In testing this just now, I noticed that the Feather value in the options bar wasn’t feathering even if all I did was fill with a solid color, so I did some more testing. The results lead to this question:

Did you change the options bar Feather value before or after creating the selection? 

What I found was:

If I change the Feather value before creating the selection, it works as expected, and the change is visible at any corners in the selection marquee because they get rounded. 

If I change the Feather value after creating the selection, it doesn’t affect the existing selection so it doesn’t get feathered.

So, see if it works better to make sure you change the options bar Feather value before you create the selection. 

You can also make a mask from the selection and use gaussian blur on that mask, then convert back to a selection (or dupe the layer, blur, and use the mask to blend with the original.)

Jimmy, I'm assuming your placement of the rectangular marquee was for demonstration...

Depending on the size of your image, 100px might not be enough.

Here's the trick I use to check on the proper feather:

[emphasis added, since my suggestion was overlooked]

1. enter the Feather amount [first]

2. then select the area to be blurred

3. press Q to enter Quick Mask mode

4. Undo if the blur is not the amount desired.

I can record a video if my instructions are insufficient.