code: private static boolean isImage(String hexString) {
      	boolean isImage = false;
      	//png
      	if (hexString.startsWith("89504e470d0a1a0a")) {    		
      		isImage = true;
      	//gif	
      	} else if (hexString.startsWith("474946383761") || hexString.startsWith("474946383961")) {    		
      		isImage = true;
      	// jpeg	
      	} else if (hexString.startsWith("ffd8ffe0")) {    		
      		isImage = true;
      	}
      	return isImage;    	
      }
docs: JPEGs start with FF D8 FF E0 xx xx 4A 46 49 46 00