function changeURL(value) {var id = document.getElementById("img_apply").src.match(/^http\:\/\/rghost\.net\/([\d]+)\/image\.png$/)[1];id = parseInt(id) +  value;document.getElementById("img_apply").src = "http://rghost.net/"+id+"/image.png";document.getElementById('idd').innerHTML = id;}
str = '<input type="button" value="Назад" onclick="changeURL(-1)" /><input type="button"  value="Вперёд" onclick="changeURL(1)" /> ID:<span id="idd"></span><br /><br /><img src="http://rghost.net/42821136/image.png" id="img_apply" />';
document.body.innerHTML = str;