WinSCP does not support thumbnails.
This right here solved all my issues. For any type of file. Thanks!
It would be great to have a small box - maybe in the lower left of the local or remote window that will show a thumb of any image you mouse-over.
To get WinSCP to open images using the Windows previewer enter the above path (without 'path-to-picture') as the path for the external editor (Where
C:\WINDOWSis the directory of your windows installation.) and then move it to the top of the list.
Don't forget to specify all the image file types you want it to open also, remembering that the functionality of the Windows picture viewer is slightly limited and doesn't open files such as Targas etc.
rundll32.exe C:\WINDOWS\System32\shimgvw.dll,ImageView_Fullscreen path-to-picture
C:\WINDOWSis the directory of your Windows installation.) and then move it to the top of the list.