QUOTE:
Each data source can be excluded from the images sitemap

that is not an option, i use joomla nativ and jreviews (joomla nativ) content with images what have to be included.
that is why i think a turn off and on function on each source would made sense for the "Recognize galleries images".
now i have to configure all other sources with the inclusions/exclusions filter too. that all just only for the "main" image of easyblog posts so that the most important image of the blogs are included - i hope you see the point of this problem