[Deff]

var obj = {"id":1, 
               "title":"HANDMADE EMERALD CUT EMERALD RING", 
               "type" :"Jewelry",
               "image":"product1.png",
               "price":"$550",
               "old_price":"$725",
               "image_ugol":"sale.png",
               "option1":"Option one",
               "option2":"Option two"
               }

function tstImg(str) {
  var Img= ['.png','.gif','.jpeg','.jpg'];
  var out = false;
  for(i=0;i<Img.length; i++){
      if((str+'').indexOf(Img[i])!=-1){out = true;break;}
   }
  return out;
}

for(var key in obj) {
  if(tstImg(obj[key])){
   alert('Картинка "'+key+'" =>'+obj[key]);
    //Тут обработка;
  }
}