Hi Susi. Thanks for reading and commenting. It sounds like you're describing a feature that some designers might call a mood board. The basic concept is to provide the client with an assortment of images that could work for their project and then let them select their favorites. Is that similar to what you're thinking? If so, one way you can do this is to actually create a scene in your Storyline project that's just for image assets that you'd like to show to clients. You would download all of the Content Library images you're thinking of using, perhaps with a short description about where and how you'll use them. Then, publish only that scene to Articulate Review and invite them to comment on their favorites. Since you can have a threaded conversation with your clients in Review this is a great way to talk through pros & cons of each image. And if they don't like one you've suggested, they can attach their preferred image to their comment so you can see exactly what look they're going for.
In terms of your suggestion to "favorite" images, I think that would also be a great feature to add to Content Library. Mind sharing your idea directly with our dev team here:
https://articulate.com/support/contact/feature-request ? I think they'd love to hear your thoughts around this—particularly your perspective as a non-native English speaker. Thanks again!