Hello @arsoftware2018
Thank you for contacting our support.
About your message, as we mention on settings page, Bialty plugin adds Alt texts to images contained between header and footer, meaning that it strictly manages alt texts of images contained inside your pages, posts and products.
Moreover, the description specifies that it uses page/post/product titles and Yoast Focus keywords defined for each of your pages/posts/products. Considering that your footer content (including your header) is repeated on all your pages and is not related to any specific page/post/product content, it explains why Bialty cannot modify or create Alt texts for images contained in these specific areas.
Hope this help.
Let us know if you need more info.
Regards