Short answer - please don't!
Editing out what is there by stamping another part of the image over in order to produce a 'prettier' picture is not what Geograph is about. We aim to record what is there, not a prettified version of it.
If people happen to be in your photo and you think they may object to the image appearing on the internet, consider if you are prepared to deal with any objections they may raise. If not, best not to submit. That said, I can only recall 2-3 images being removed from view because of objections raised by people (known to the photographer) who appeared in them - in the 11 years since the site started.
Some submitters do blur out legible vehicle registration plates. Opinions vary as to whether this is necessary or desirable but it is not a reason for rejection if subtly done.