As with the videos, we make it clear when requesting the slides that we’re going to distribute them, and we abide by the wishes of those who opt out.
Unlike the videos, we (Open Robotics) don’t want any ownership of the presenters’ slides. We just want the presenters’ permission to distribute the slides. We don’t declare any license regarding the rights of others to use or redistribute the slides that we post.
As a result I believe that we’re in the default situation for copyright of “all rights reserved”, which is to say that individuals can download and view the slides but cannot, for example, redistribute them, perform them (i.e., give a presentation using those slides), or create derivative works from them (e.g., copy slides, images, or text from slides verbatim into other media) without permission of the presenter (and/or possibly the presenter’s employer).
Like with the videos, for future editions of the conference, we’ll consider additional language in presenter interactions and on the website to make the situation more explicit.