User pictures have transparency information removed

When uploading user pictures as PNG images the transparency information is removed and replaced with the colour black.

Steps to replicate:
1. Bulk upload a list of users
2. Bulk upload a list of user pictures in PNG format with transparency information. (Sample png attached)
3. View user profile
4. Note that the transparency has been replaced with the colour black

Expected output:
User images that are uploaded as PNG images with transparency information should retain the transparency.

Actual Output:
User images that are uploaded as PNG images with transparency information have the transparency replaced with the colour black.