Their website says:
You hereby agree to download "Digital Goods" for private, non-commercial use only and that you will not copy, redistribute, transmit, assign, sell, broadcast, rent, share, lend, modify, adapt, edit, sub-license or transfer the "Digital Goods" to anyone else.
Which I take to mean that you can't upload them to WikiTree. Most tombstone pictures can't be uploaded unless you take them yourself. Or - the photographer gives you permission.