Why won't my photo fit in the slideshow?
Think of the slideshow as a physical picture frame and your image as a physical picture. The frame is a set size and regardless of how important or beautiful the picture is, there is no guarantee that your picture will fit into the frame.
In the case of the home page slideshow, various frame size for the picture are 1920x480 pixels (4:1), 975x325 pixels (3:1), 1440x480 pixels (larger 3:1), or 650x325 pixels (2:1). The orientation is landscape, so photos that are wider than they are tall will fit better. Photos that are portrait oriented will have to be cropped significantly to fill that area.
NOTE: Photos that are wider than they are tall will fit better into your homepage slideshow.
To illustrate this, say you have a photo of a chalice you want to put in the slideshow for some special event.
You'll notice this image is portrait (vertically) oriented. In order to fit into the home page slideshow, it would need to be cropped. On the left is the cropping for the 650x325 slideshow. On the right is the cropping for the 975x325 (wider) slideshow. The light part is the part you would see in the slideshow. The darkened area would be cropped out.
As you can see, the cropping of a portrait image is pretty severe.
It's possible to digitally resize an image like so:
But as you can see, the distortion to the image is unacceptable, and so we don't provide that as an option. For inanimate objects you can get away with a little distortion, but on a human face, the results are...comical.
When taking a picture for your slideshow, make sure the image is wider than it is tall (such as a panoramic shot) so that the amount of cropping you'll need to do is kept down to a minimum.