Download this filter and unzip it into your plugin directory in a new folder called AAA.

Download Transparent Frame and Transparent Vignette in a single zip file.

Use this filter only on layers.
It works by making the edges of the image transparent, which allows the underlying image to show through.
The underlying image blends with image above. Apply any effect you like to the lower image.
The example below shows that the middle layer has been blurred and toned purple to blend at the edges with the color photo.

The lower layer, which will blend at the edges, doesn't even have to be the same image as the upper layer.
The possibilities for blending images are infinite!