A plugin for JOSM that acts as a WMS server for Yahoo satellite imagery. Used with wmsplugin.

From the announcement on talk:

With this new plugin, you can now work with Yahoo satellite images inside
JOSM, the same way the applet or the flash editor does. It is a port to java
of the perl script that Frederik Ramm made a couple of months ago, so it
uses the same approach: spawn a browser window that asks Yahoo the images
using its API. However, this plugin works in windows too.

To use Yahoo imagery, follow this steps:

1.- Download and install YWMS from [1].
2.- Download and install/update WMS plugin from [2]. IMPORTANT!!: upgrade if
you already have this plugin.
3.- Activate both plugins in JOSM and restart.
4.- In preference settings, Yahoo tab, set the path to firefox executable,
the name of a new profile for firefox and click  "create". This opens a new
browser window. Click "Make changes" and accept the question. Close the
browser.
5.- Go to your favorite area, and click the menu option "WMS -> Yahoo" .
6.- Enjoy

Any modern Gecko browser ([3]) should work, not only firefox. However, I
have only tested firefox (>1.5.)