How to restor joms wms stored image file ?

I use Yahoo wms to dowload satellite image to complete tracking work.
The matter is when I want to save downloaded files and never can restore them for a new session with josm.
Why ?
If I do a mistake, what is it?

The license on the Yahoo! imagery does not allow us to store (or cache) the imagery locally. So the plugins for JOSM do (should) not support storing the imagery locally.