Are you trying to preview a lot of images in a folder so you know which one to open up? However they are displayed as icons rather than pictures? It is so much easier if you can see all images as a thumbnails so you can know which one is the one you looking for. Read below so you can preview all of them rather than going through one-by-one!
1. Navigate to the folder you were looking at.
2. Switch to View tab and Select Large icons (It can be other sizes like Extra Large and Medium).
3. As you can see they are still showing as file icons but not pictures.
4. Select Options from View tab.
5. In Folder Options, Select View Tab.
6. Untick "Always show icons, never thumbnails".
7. All done! Grab a cup of coffee and view the pictures at once!