Lowercase image format jpg,png,jpeg do not display

Iam experiencing a problem of the images with the lowercase format (jpg,png etc)can not displayed but with uppercase format (JPG,PNG etc)are working properly, I use default image field ,I need your help to eliminate this issue it is very annoying ,I have to change to upper for every picture otherwise I get this error msg “You are not authorized to access this page.”.

Source: https://www.drupal.org/project/issues/rss/documentation