var ar = new Array("<IMG SRC=html/east_river_park177.jpg width=177 height=101 border=0>", 
"<IMG SRC=html/tribeca_park177.jpg width=177 height=101 border=0>",
"<IMG SRC=html/wall_st_west177.jpg width=177 height=101 border=0>");

var num = Math.floor(Math.random() * ar.length);
document.write(ar[num]);