More Photoshop Masking. 3 Gradients

Open a picture in Photoshop.

Then drag another photo into the document from your desk top.

Put the layers into the order you desire.

Withe the top layer selected, click Make Layer Mask

Your layers should look like this.

With the Mask thumbnail selected, select the Gradient Tool from the Tool Panel

Go to the top of the screen and select Radial Gradient

Then click the Edit Gradient thumbnail.

Alter the Gradient so that it is White on the left hand side and Black on the right hand side.

(You do this by clicking on the little squares blow the Gradient Strip.)

Now place the Gradient Tool in the middle of your picture and drag out to create a mask.

Something like this.