A photographer selling his work in Union Square made it clear where he stands on the Parks Department’s proposed rules to limit the number of vendors in various city parks, including Union Square Park, Central Park and the High Line. Under the proposed regulations, only three vendors, including so-called free-speech-protected vendors — covering those selling printed matter, art and expressive materials — would be allowed on the High Line and only 18 at Union Square Park. The department says the large number of vendors detracts from people’s enjoyment of the parks. Artist vendors in the group A.R.T.I.S.T. (Artists’ Response to Illegal State Tactics) are gearing up to fight the proposal. A public hearing will be held on the issue on Fri., April 23, at the Chelsea Recreation Center, 430 W. 25th St., starting at 11 a.m.