Delete Pictures
Thumb Image lets you delete it without removing the original. Just select and delete.
Index Pictures
Indexes are added to Pictures for fast lookup of alternates, originals, and thumb images.
Dialog Buttons
Dialog Buttons are larger to have more space for names and icons and rounded corners.
Rounded corners are more rounded in newer systems and system objects like buttons. Larger buttons are needed to fit the names and icons that fit into previous buttons.