You're confusing copyright licencing with model releases, they are separate and not actually related.

Licencing and copyright govern who is permitted to have the images and if/where/when they can reproduce a work.

A model release indemnifies a licensee should they show the subject(s) endorsing a viewpoint that the subject does not hold or shows them in a negative light. Without this indemnity they risk Libelling the subject who would be able to seek redress and damages through legal channels with a reasonable chance of success.

For more information see:- What can and cannot be legally done with editorial photos?

If your image has been taken on the street then some additional caveats may apply...

Most regions operate under the rule of an "expectation of privacy" and usually if you can see someone from a public place then you're free to photograph them, but that does not apply everywhere. Obviously you definitely should not distribute it if you shouldn't have taken it as you're publishing evidence of your crime.

Also if any person is identifiable in the image, prominent or otherwise, then Data Protection rules may come into play since while personal data is frequently considered "information necessary to identify and locate a person", this depends on jurisdiction. Some would consider a clear photo of a person's face sufficient.

Even though you may be legally permitted to post/sell/share images you've taken it does not mean that it is ethical to do so (for example if the subject has specifically asked you not to)... and even if you are in the right the cost of defending yourself in a civil action may be significant even if you win. Sharing them on flickr/500px is not usually an issue but as with any legal question, if you're unsure then you should retain the services of a local expert.