As to size of pictures, use the space if absolutely needed for detail-rich images. however, most of the time we can appreciate a picture far better, even undersized, where the image can be embedded centrally in white space as in a gallery. Then one can appreciate better the sweeps and gestures of the pictures make up that often are masked when one has to scroll an image to see the entire work! Of course, one can use keyboard strokes, ("Apple -"), to shrink the image, but that doesn't provide the white space.
Asher