Well the traditional approach is to contact them and secure their permission. But as you alluded, that doesn't scale. So perhaps there's a startup opportunity

Well the traditional approach is to contact them and secure their permission. But as you alluded, that doesn't scale. So perhaps there's a startup opportunity here, for a system that secures permission from people who are ok with their content being reproduced without their prior consent. Perhaps there could be a service that creates a list of web sites where the content is licensed Creative Commons. Then, if someone was going to create a web app like this, they could filter that list against their web app to only include sites that have been licensed creative commons.