Normal – image is positioned in the upper-left corner of the PictureBox, and any part of the image that is too big for the PictureBox is clipped.
StretchImage – image will stretch or shrink to fit the PictureBox.
Zoom – the image will be stretched or shrunk to fit the PictureBox but the aspect ratio in the original is maintained.
AutoSize – the control will resize to always fit the image.
CenterImage – the image will be centered in the client area.