Update um-image-upload.php

to prevent overwrite of multiple image uploads with the same name, I've added the $id to the filename just prior to the sanitize_file_name() call.

core/lib/upload/um-image-upload.php

@@ -35,7 +35,7 @@ if(isset($_FILES[$id]['name'])) {
     if(!is_array($_FILES[$id]['name'])) {
 	
 		$temp = $_FILES[$id]["tmp_name"];
-		$file = $_FILES[$id]["name"];
+		$file = $id."-".$_FILES[$id]["name"];
 		$file = sanitize_file_name($file);
 		 $ext = strtolower( pathinfo($file, PATHINFO_EXTENSION) );
 
@@ -55,4 +55,4 @@ if(isset($_FILES[$id]['name'])) {
 } else {
 	$ret['error'] = __('A theme or plugin compatibility issue','ultimatemember');
 }
-echo json_encode($ret);
+echo json_encode($ret);