Changing all PNG files in site to JPEG? Is there any way to instantly change all the PNG images in a D7 site to JPEG (with or without backup creating)? By all PNG images I mean to those uploaded via image-field as well as those uploaded via CKeditor.

Going through page after page and changing them manually would take much time, therefore I'm looking for a more automatic way.

Thanks for your advice.
With imagecache_actions module you have several actions. One of then is "File Format switcher" so you can serve JPEG instead of png without converting the source images.

For more information:
https://www.drupal.org/project/imagecache_actions