When you snap a picture using your digital camera, not only the camera saves the actual picture data but it also stores some meta data with the picture file. This metadata can be of IPTC (International Press Telecommunications Council) or EXIF (Exchangeable Image File) type. This metadata can contain information about the picture such as the camera make and model, whether the flash was fired, what was the focal length used, the longitude & latitude coordinates of the place where the picture was taken and the time when the picture was snapped. Usually you need an image viewer application like IrfanView or XnView to have a look at this metadata, but for this you first have to download the image file to your hard drive and then use the image viewer to view the metadata.
If you want to save time and want to view EXIF or IPTC data for any picture right inside your web browser using the Exif Viewer extension for the Mozilla Firefox web browser. After you have installed this extension, all you have to do is open an image in your Firefox browser, right-click on the image and select Exif Viewer from the context-menu. If a website is using protection mechanism to prevent users from downloading those images (usually by using an overlay just like Instagram does) then it won’t work.
This will open the Exif Viewer window displaying all the information about that image file. The information can be viewed in the list form or the table form. All the metadata information is categorized properly so that you can click on IPTC, Maker Notes or IPTC Core etc. to quickly jump to the relevant section. And if you want to view the histograms for the image then you can select the Show Histograms checkbox which will display many different histograms for the selected image.
You can get the EXIF Viewer extension for Firefox from https://addons.mozilla.org/en-US/firefox/addon/exif-viewer/.