Here's one method I found to create a kind of fade in effect for a photo. This technique faded an image from the left side, from white.
Figure 1 is the image I started with. First, I created a new layer. then select the left handed portion of the frame that I wanted to represent the fade in. In this image I wanted it to fade in completely before it got to the subject.
I wound up with a selection about the size in Figure 2. I set the color to black, then did a Paint Can fill with Gradient, ensuring it went left-to-right, light-to-dark. I then selected the rest of the image and did a Paint Can fill with solid black.
Figure 3 is the end result of that layer. Then I create a new layer on top, select the entire image from the canvas layer, cut, then paste to the top layer. Basically I want the image on top of my gradient layer. I then set the layer attribute of that top layer to 'Screen', which creates a merge of the two layers. I also wanted a little more white at the left of the image so I added 10 pixels to the left edge of the canvas.
Figure 4: Voila!
Figure 5 is the same thing, but using 'Lighten' instead of 'Screen' for the layer attribute. It appears to cover more on the left edge, while also making some of the colors more intense at the same time. A different flavor of the same thing.
Another variation in Figure 6, fade from black, was done by using 'Gel' for the picture layer attribute, and doing a Negative on the gradient layer. Not sure if it works well in this case only because the original image has so much black.
Finally Figure 7 is one with an additional layer BELOW the original fade layer. On the original fade layer I added the right side gradient dark-to-light using the paint can after deleting all the black color first. Then the new layer below uses a top-to-bottom, dark-to-light gradient on about the last 20 percent of the image. Again, Paint Can Fill the rest of the layer with solid black. To get the two layers to work together, set the top gradient layer's attribute to 'Magic Combine'. By the way, I also added an additional 10 pixels of white at the bottom and at the right.
...and Figure 8 is essentially the same thing, but taking a large bleach eraser with a very low opacity setting and skirting the edges for a looser look.