Configure Windows 10 to show thumbnails of picture files in Explorer.

1. Open Explorer ("My Computer")
2. Click on "View" on the menu bar at top.
3. Click the down arrow on the "Options" item.
4. Click on "Change Folder ans Search Options".
5. Click on the "View" tab.
6. Uncheck the "Always show icons, never thumbnails" box.

  OR

1. First right-click on Computer on the desktop and choose "Properties". 
2. Click on "Advanced System Settings" on the left side.
3. Click on the "Advanced" tab and then click on "Settings" in the "Performance" box.
4. Make sure the "Show thumbnails instead of icons" box is checked.