image widgets not recognised by SEO?

Hi, I am trying to make my site SEO-friendly with WordPress SEO Yoast. Almost all the images I have on my site, I have displayed in image widgets. But it looks like WordPress SEO doesn't look at those images. It only sees the images that are posted in a page itself. Also when I generate a XML sitemap, only those images which are in a page itself, are shown, but not the images in the image widgets. (I have Catch Evolution Pro and am still working on Wamp server now)