Does anyone know what the laws are around this? Do I need to license the rights to use the photos if they are just thumbnails?
I haven't be able to find anything through my own searching.
For example, CNN's Terms of Service reads:
"You may not modify, publish, transmit, participate in the transfer or sale, create derivative works, or in any way exploit, any of the content, in whole or in part. You may download copyrighted material for your personal use only. Except as otherwise expressly permitted under copyright law, no copying, redistribution, retransmission, publication or commercial exploitation of downloaded material will be permitted without the express permission of CNN and the copyright owner."
The other sites you liked have similar clauses.
You may only use the images and article excepts if your usage is Fair Use, which you can learn more about here. http://fairuse.stanford.edu/overview/fair-use/
I suspect your "news aggregator app" is however, NOT FAIR USE, which means you cannot pull their content without their consent.
IANAL, but work around a bunch of them.