This might not work so well if the layer was too dark or light. Best to average the layer lightness to mid grey using curves.
The reason: Everything in the Oberlay family is a contrast effect. The darks act to darken, the lights act to lighten. Hence an average of mid grey will be least intrusive.
This is different to the multiply family, which can only darken, or the screen family which can only lighten.
* duplicate your photo layer
* apply a Gaussian blur to the duplicate (5-10px, depending on total resolution)
* set the blend mode of the duplicate layer to "overlay"
* fiddle with the opacity to reduce the strength of the effect