Crop an image and discard the parts you cropped.
Area that's been cropped.
To delete the trimmed portion, first click the Compress Pictures
button on the toolbar.
Then select the Delete cropped areas of pictures
option in the dialog box.
Another option you have in the Compress Pictures dialog box is to delete "trimmings" from an image that you have cropped. Using this option, Delete cropped areas of pictures, can significantly reduce the size of an image file.