I think it will be best for you to work on these parts one piece at a time. The first thing you should do is update the register users page to add in the file upload functionality. To do this you need to open the registration page in DW and add in a file field to the form. Once you have added the file field to the form you will need to select the form tag and add the enctype attribute to it, it will need to be set to multipart/form-data like this:
I think it would be best to start on this part and make use of the How To that is on the Universal Email support page, here is a link:
It describes how to add a file upload to a DataAssist page, this is the one that you should take a look at.
Once you have completed this part you can move onto the next part. As for having the image show up on this page after it is uploaded that might not be so simple. The image will only upload when the form is submitted, this same action will insert info into your db and send the user to the next page, the profile usually. You can display the image on the profile page if you would like.
Once you are past this let me know and we can move onto the next part.