If you want to change the allowed image extensions for product images in Magento you will find out that they are hard coded in Mage/Catalog/Model/Product/Attribute/Backend/Media.php and Mage/Adminhtml/controllers/Catalog/Product/GalleryController.php
However, I found an observer that allows you to change them along with other configuration of the uploader. This post explains how to create an extension to allow uploading of SVG files. Foundations of Magento extension develoment are presumed.