Even "Paint" works...
Right-click image,
Copy,
Then open copy in Paint or program of your choice,
Save As whatever you want to name it,
Change size to 50 X 50,
Save As .jpg(important!),
Close program,
..and you'll have the renamed copy as a .jpg to use!
[usually, each of my brain cells finds it hard to locate the other, and I need explicit directions like this or it can take up to three years for me to understand]
