var conf = {
	className : 'btn',
	postfix : '_f2'
};
$('img.'+conf.className).hover(function(){
	this.originalSrc = this.src;
	this.src = this.originalSrc.replace(/(\.gif|\.jpg|\.png)/,
																			 conf.postfix+"$1");
},function(){
	this.src = this.originalSrc;
});