Before you can access the Shooting Data Display mode on your Nikon D7100, you must enable it via the Playback Display Options setting option on the Playback menu. In this mode, you can view up to four screens of information, which you toggle among by pressing the Multi Selector up and down.
The fourth screen appears only if you include copyright data with your picture.
Most of the data here might not make any sense to you until you explore the exposure, color, and other advanced settings available on your camera. Still, here are a couple of data points:
The top-left corner of the monitor shows the Protected Status key and Retouch Indicator icon, if you used these features. Otherwise, the area is empty, as in the figures.
The current folder and frame number appear in the lower-right corner of the display, as does the Image Area setting (DX or 1.3x crop).
The Comment item, which is the final item on the third screen, contains a value if you use the Image Comment feature on the Setup menu.
If the ISO value on Shooting Data Page 1 (the first screen) appears in red, the camera is letting you know that it overrode the ISO Sensitivity setting that you selected in order to produce a good exposure. This shift occurs only if you enable automatic ISO adjustment in the P, S, A, and M exposure modes.