You'll need to use the $image variable in your conkyrc, there is help here: http://conky.sourceforge.net/variables.html
There are also posts on displaying images in conky in the conkyrc thread somewhere. You might want to ask again in that thread whilst also posting your conkyrc: http://ubuntuforums.org/showthread.php?t=281865
You can also look at examples with the forecast script which work the same way here: http://conky.linux-hardcore.com/?page_id=2487
Also, it is worth mentioning that you have an awful amount of execs for the forecast and banshee scripts, you only need one for each if you use templates with the scripts. The example files for both forecast and banshee scripts will explain how, read through the first post here and at the forecast thread for info on where to look.
You have a bit of reading to do but it will be worth it!
Note: you need version 1.7.2 of conky to use this feature (karmic version by default, if you're no using karmic then find a suitable deb or compile conky yourself)
Hope that helps