I think it's a fantastic idea and you've put a lot of thought into the type of quality you are seeking for the project. One of the things that came to mind though was http://steemimg.com which already allows members to share images, but also use the picture link for their Steemit articles, especially if they don't have a website or FTP client. There are a couple of issues I see with that site. 1. quality is not always good. 2. i think there may be copyright issues with many of the uploaded photos.
I personally use pixabay for CC images and art and I know that when submitting a photo for their site, they have very specific guidelines and a team of people who review submissions. Something to think about.
Thanks for a brilliant response.
I suspect you are right about the copyright issues for uploaded photos. Ultimately it is up to the poster to ensure that they have the appropriate permission to use images - for this tag the guidelines are very clear and if they submit images they don't own then they are responsible for breaking the law not the people who might use them afterwards.
Although it could be integrated with a particular host that is not absolutely necessary and I think people should have a choice of hosts which they can use.