Thumbnails are small previews of images you have in different folders on your computer. If you don't like them, they can be disabled. Just check out this article:
Remove previews from Windows Explorer.
The size of the thumbnails is a default one, and it can not be modified by normal methods.
Why change the size?
Well maybe because you have a lot of images and you’d like to view as many as possible at once.
To change the size of your thumbnails you’ll have to modify the system registry. I want to emphasize the fact that modifying your registry can be dangerous, especially if you do it wrong, and that we can not be held responsible in any way for the damage you may inflict on your Pc.
You will have to start the registry editor. You can do this by clicking on the Windows Start button, and then “Run…”. In the edit box which appears enter “regedit” without the quotes and press enter.
A tree like list will appear. You will have to navigate your way through the branches to HKEY_LOCAL_MACHINE -> Software -> Microsoft -> Windows -> CurrentVersion -> Explorer. In the right side you will have to create a DWORD entry named “ThumbnailSize” (without the quotes). You can do this by right-clicking an empty space, and clickikng on New -> Dword Value (see image below) and entering the name.

After you’ve created the entry, double-click it an entry a value between 32 and 256 (where 32 is the smallest size and 256 the biggest). The entry should look like this:

Now go to the folder with your images and see the difference. It should be from this:
To this:
If you can’t see any difference, restart your PC for the settings to take effect.
If you want to reset the thumbnails to their default size, go again to the key entry created above and delete it.
Hope this helps!
Posted by: Nitro on March 9, 2006 at 18:03.