As a member (not a subscriber), you will not be able to upload to the Monthly Shooting Assignment gallery, but you can upload an attachment to a post in this thread.
The original photographs must have been taken on film, but conversion of that film image to a digital file that can be uploaded can be done in a number of different ways:
1) Scans from prints are always good;
2) Scans from transparencies are good too;
3) Scans from negatives are also acceptable.
There are restrictions on the types and sizes (both file sizes, and pixel dimensions) of digital files that can be attached to a post. If you click on the paper clip icon from the advanced Reply to Thread screen the acceptable file types and sizes appear.
You can also link to an image that is already posted to the web.
Hope this helps. Ask away if you have more questions.
PS This is even more fun if you become a subscriber, and can post to and review at leisure the galleries .