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.
You may be ok with it, but what about all the other folks out there? Checking with each of them would be the right thing to do, but complicated.
The culture of lifting original information and data regardless of the wishes of the original creator is a bad thing.