Ok so I re-read your post at the beginning you say that you get the image in the browser.
Hoiw does the other camera work?
Does it point to a cgi file as well?
cgi files are website scripts not images.
wget and the browser will download the image generated by the cgi script but not the sitemap “binding”
An alternative way to do this would be to get the exec binding to execute the wget command and store the image in your /conf/html folder and then point the sitemap image to that file.