Step 1
Open a photo into Photoshop. This is the image that will be used for this tutorial:

Step 2
To begin, create a new layer (Layer> New> Layer) and change blending mode of the new layer to Screen. This new layer is where we will create the rain texture.

Step 3
With the new layer selected, press Ctrl+F5 to open the Fill tool or open the Edit menu and select Fill. In the Fill tool, select 50% Gray from the drop down menu and click OK.

Step 4
Open the Filter> Noise menu and select Add Noise. In the Add Noise tool, leave the default settings, check the Monochromatic option, and click OK.
