Do not forget the thumbs directory when returning the images paths

htdocs/product/class/product.class.php

@@ -2946,7 +2946,7 @@ class Product extends CommonObject
 					// Objet
 					$obj=array();
 					$obj['photo']=$photo;
-					if ($photo_vignette && dol_is_file($dirthumb.$photo_vignette)) $obj['photo_vignette']=$photo_vignette;
+					if ($photo_vignette && dol_is_file($dirthumb.$photo_vignette)) $obj['photo_vignette']=$dirthumb . $photo_vignette;
 					else $obj['photo_vignette']="";
 
 					$tabobj[$nbphoto-1]=$obj;