These are similar to the non-exclusive licensing terms as used by Facebook and other sites where they provide a service (a website and image display platform) at no fee to the user. You're not giving up your original ownership of the image. Your 'legal' rights to ownership and copywrite are not impacted either, although you're always encouraged to properly and formally register your US-based copyright with the US Copyright office at:
https://www.copyright.gov/If you consider these terms of use an issue, you have multiple options:
1) Never post any images to this photography-related site.
2) Never post your best images to this site.
3) Never post a original or large resolution file, even if you don't "store the original". Instead, resize the image for online posting as discussed at:
Recommended resizing parameters for digital images4) Use embedded links to share images here at UHH that reside on a "more" secure site such as your own website, Flickr or similar. Use the link "Show Tags" below the text box when editing and investigate the "url" and "img" options to embed an image link from UHH to your website / image source where the actual image file resides.
Finally, for those who attach
and store fully-edited high-resolution image files, it's more likely that the wider nefarious internet will
take your images rather than the UHH site owners will
reuse these image files. Note that no one on the internet is required to provide credentials to access this site. You need a user and password to post to the site, but anyone anywhere can come and download your file attachments, with no tracking nor acknowledgement.
This same "open site" aspect of UHH should also prevent you from ever sharing personally identifiable information, like phone numbers, street addresses or email addresses. That information should always be shared only via credential-based Private Messages (PM) or your personal email, not posted publicly on UHH.