Probably the issue is that camera images and print paper are simply different shapes.
Digital cameras are mostly either 3:2 or 4:3 aspect ratio (image Shape). Shape is different than Size. Regardless of size, 3:2 is 1.5x longer than wide, and 4:3 is 1.33x longer than wide. These are shapes.
Standard print paper Shape is 8x10 (1.25x longer than wide) or 5x7 (1.4x longer than wide) or 4x6 (1.5x longer than wide). Most often simply a different shape than our image.
So, we generally always have to first crop the image to match the desired paper shape. Necessary knowledge for all of us. More detail at http://www.scantips.com/lights/resize.html
You might ask the photographer if he can furnish uncropped images. But possibly he already did, and instead cropped in the camera when shooting, and just stood too close to allow proper printing. And the camera shape rarely matches paper shape.
You want the image wider. Normally that means careful tedious editing to fill in width of the proper colors to match the background.
However, you said White, which will be very easy in Photoshop. Just use menu Image - Canvas Size (Canvas size is the paper size). You can change dimensions to be Pixels, Percent, or inches however you want to work (but this is relative to the size it is now). Type in new dimension of the paper for the dimension you want wider. Or a pretty wide dimension, and you can crop that later. Leave the Anchor (alignment) dot in the center and it will on both sides. The fill color is specified as Background Color or Foreground color, but you can specify White there.