As always, it depends. You give your users pretty much permissions - this causes responsibility in form of constant surveillance.
I see some causes to dispense with user generated content in the form you describe. The causes are i. e.:
- User could upload images containing malware,
- User could upload child porn,
- User could upload images causing DMCA to your site,
- User could add tags not matching content,
- User could add redundant tags, as duplicate of existing tags, just in different spelling,
Even if everything goes OK, you'll be forced to set all of your tag pages as
noindex, because such pages would display same images in slightly different sorting and generate nearly duplicated content.
The optimal SEO-minded way would be imho:
- instead of tags use categories, where images would be displayed in unique order,
- !!! don't publish images uploaded by users automatically !!!. Firstly look at images, check, whether images and image names given by users are OK. Then apply meaningful
alt tags, sort images into correct category and publish.