How to submit photos taken in a US National Park

Hello,

Just so that we are all on the same page, what was the actual reason that came with the email? Was it something like 'non-compliant', 'Technical issues'...?

Most likely your image was rejected for technical reasons, not IP issues.

US National Park Photography Rules (Dept of Interior)

https://www.backpacker.com/skills/9-things-you-need-to-know-about-national-park-photography-rules/

You must obtain a permit for commercial photography, video and/or film shoots that use models, actors, props or sets.  Permit costs range from $50/day for single still shots to $750/day for movies. If you need a permit and don't have one,  you could be on the hook for $5,000 fine or 6 months in jail.  Wilderness Areas have separate rules and may require additional permits.

You do NOT need permission to sell your images commercially.  

Hope that helps.

Why do you assume that this is not about image quality? What is the refusal reason? I think the image is over processed. It looks like an HDR image. You should get a more natural look.

As for the authorization, you should contact the park to know what limitations this site has. You need either to show that no authorization is needed or you need to have a signed release. In both cases, only the park administration can give you a hint on this.