Windows Explorer has an excellent feature like any other file manager to show thumbnail previews of pictures and videos in any folder. To make sure that the thumbnails show instantly every time you open a folder, it caches the thumbnails. Unfortunately, sometimes it fails to generate a thumbnail for some files, or continue to show an older thumbnail preview even if you updated the picture. Here is how you can force Explorer to refresh the thumbnail.
Windows supports viewing commonly used picture and video formats as thumbnails in Explorer folders. But for less common formats, it does not generate thumbnails. Also, in modern versions of Windows, the programming interface for generating thumbnails has changed compared to older versions such as Windows XP, so the old shell extensions to show thumbnails no longer work. Let's look at some modern ones that do work and generate thumbnails for all possible formats you might need.
As you might be aware, Windows 7 introduced a redesigned taskbar which abandoned much loved classic features but introduced some really nice improvements like large icons, jump lists, draggable buttons etc. The taskbar does not have many configurable settings exposed in the GUI to tweak its behavior but there are some hidden secret registry settings which you can fine-tune.