Web site window appearance on screen

Hi everyone,
Im having a problem with the viewing of my web site, https://www.stevewinstonphotos.com.

Its a web site to display and ideally sell my photos, but when you view the web site on a screen, and go into the galleries, particularly, the “Contemporary Eye” Gallery, the main image which is the background is cropped to the extent of the screen, so that you cannot see the image in its entirety.
HOWEVER, if you then start to resize the browser window, the entire image starts to come into view – try it.
To see the full image, you need to resize the browser window to something that is long and narrow – hardly ideal for trying to sell photos.
Is ANYONE able to offer any advice as to how this problem can be overcome, so that anyone visiting my web site, regardless of the size of their browser window or their screen, can see the entire image that they have selected in the background?
Any relevant advice will be very much appreciated.