Well i can help you a little if you know php/html a little bit.
You should proceed like if you want to add an extra field to community builder. Like described on this page:
http://www.ghanja.be/en/add-user-frontend/add-extra-fields-to-auf-for-cb.html
For your fieldname you will choose the fieldname
avatar which exists in the
_comprofiler table.
The database field avatar will contain the filename.
For example:
123456.jpg
CB will search for the images in:
your_public_html/images/comprofiler/
So thats were your images should be uploaded.
Now you know enough to create a file upload script which uploads the images to your server at the specified location.
The script will also need to resize the avatar and create a small version of it in the same folder with the same name but with the letter "tn" before it.
structure:
Filename:123456.jpg
Resized Filename:tn123456.jpg
I hope this will get you started.
Kim