You may need to show pictures like this one 23458934z5689.jpeg as mountain.jpeg in src attribute. But pathauto module does nothing with picture synonyms. In this article, I would tell you how to fix this shortly.

Solution:

Please use one of the modules below to create synonyms for your site pictures:

Pathologic (http://drupal.org/project/pathologic) – manage src attribute (see 3th parameter)
Imagepath (http://drupal.org/project/imagepath) – even better for our purpose
Uploadpath (http://drupal.org/project/uploadpath) – renames a picture based  on a template for all uploaded files and use standard Upload module.

Good luck!