Fade to white?

I see 2 options that can be used:

- The Overlay (watermark) effect: the overlay image should be a fully white image with transparency. The transparency channel should be 0 at the left (fully opaque, giving white in the resulting image) to 255 at the right (resulting in the pixels of the original image being shown unchanged).
- A combination of the Define Canvas (to define a white background) and the Image mask effect to add transparency to your image. In your case the mask should be a black & white image that goes from black at the left, via gray in the middle to white at the right end.

Both effects do not support the stretching of the mask/overlay, so you should first (crop &) resize the image. Grayscale images that can serve as mask can easily be found via Google (images).

Note: if you want fade to white because your background is white you can also use the 2nd option without the define canvas effect, but with a convert image format effect that converts the result to png. This allows for other background colors or other items on the background to become partially visible, but at the cost of bigger image files.