I’m guessing that the “no professionals” rule is to avoid complaints from people who object to signing over unlimited publication rights to BCC, on any submitted images – not just those that are selected for a prize. This pretty much means you won’t be able to sell that image again, and certainly not to any magazine that might ask for an exclusivity window. It’s a pity that the publication plans aren’t spelt out in more detail really (eg. “All entries will be available on the website as screen-sized jpg images for no more than 3 months after the closing date. Winning entries will be required to grant print publication rights for our community newspaper.”). The lack of clarity might make for shorter rules (arguably) but it should dissuade people, especially students who aspire to sell work, from entering.