I am going to show you how to using the layer mask effect for this tutorial. We are going to take the below image and, using a layer mask, get rid of the edges.

(Image is from Deviantart stock photos)

Step 1: Open up the image provided above. Double click on the image layer, and when the layer dialogue comes up, just press OK. You have now converted the image layer from a background layer to a normal layer.

Step 2: Go to Image > Canvas Size, and change the canvas' dimensions to 550x424. There will now be a checkered(transparent) background outside the image. Note: it is not required that you increase the canvas size, but it does help in this tutorial.

Step 3: Create a new layer and drag it below the image layer. Fill the new layer with white using the paint bucket tool. (You can also fill it with white by having your foreground colour set to white and pressing alt+backspace, which fills the layer with the foreground colour.)

Step 4: Select the image layer, and then click the add layer mask button, which is on the bottom of the layers window, and has a square with a circle in it. You will see that a white square has appeared next to your image on the layer window.

Step 5: Click once on this white square (the layer mask) to make sure it is selected. Once you have done that, select the gradient tool and choose radial as the type of gradient which will be used. Select black to transparent as your gradient colour.

Step 6: Making sure the layer mask is still selected, click and hold somewhere in the middle of the eye. Now drag downwards, making sure the gradient line doesn't pass the borders of the image. If you do this, then the borders will still be visible once the gradient mask is done. If you make a mistake, just undo it and try again.

Step 7: Now that you have the gradient created on the layer mask, you have to invert the mask so it looks correct. Do this by selecting the layer mask on the layers window, and pressing control+i. There you have it, the image now has a layer mask applied to it!