Have you ever noticed the little info tooltip that appears when you hover your cursor over thumbnails in Grid view (G) or the Filmstrip? A lot of people don’t realize that this is connected to the Info Overlay that appears in Loupe view of the Library module.
Head over to View>View Options, and click the Loupe View tab (notice that if you were in Grid view, Lightroom switches to Loupe view when you click that tab so you can see the overlay).
There are actually two Info Overlays that you can configure to show different groups of information. Beyond the image info tooltip that appears when you place your cursor over a thumbnail in Grid view or the Filmstrip, the Info Overlay appears in the upper-left corner of your photo when you’re in either Loupe (E) or Compare views (C) in the Library module, or when you’re in Develop. You can easily show/hide the overlay and cycle through the two Info Overlay displays by pressing the I key. You can toggle the overlay on/off by pressing Command-I (PC: Ctrl-I).
The information you choose to include will depend on how you plan to use the overlays. For example, I find it helpful to include the File Name when using Compare view to easily distinguish between similar and multiple versions (RAW, TIF, JPEG) of the same photo, and I find Cropped Dimensions helpful when using the Crop tool to see the final pixel dimensions that result from a particular crop. If you’re prone to using the Filmstrip to navigate through photos while in Loupe view, you might find it helpful to check the Show Briefly when Photo Changes box under your preferred Info Overlay (you first have to uncheck Show Info Overlay to enable the Show Briefly option). This way, each time you select a new photo, you’ll see that selection of data appear briefly in the upper-left corner of the photo. You can still use the I key to override this option and cycle through each state or keep the overlay on for good.
If you only care about what data shows in the tooltip and don’t want to always see it in Loupe view or Develop, configure the info you want to include in either Info Overlay 1 or 2, then select either Info 1 or Info 2 in the drop-down menu. Exit the Library View Options dialog, and press Command-I (PC: Ctrl-I) to hide the overlay in Loupe. Now, you should only see it in the tooltips, and when you want to see it again in Loupe, press that same shortcut again to bring it back.