Try this:
In Salesforce, go to Visualforce pages and find the UploadImage VF page that has the skuid namespace. Clone this page - keep everything the same (name, page markup), except now it won’t have the skuid namespace.
Next give access to your new Visualforce page to your guest community profile.
Then try your upload.
More info here, in the pre-requisites section:
https://docs.skuid.com/latest/en/skuid/deploy/salesforce/visualforce/skuid-page-visualforce-componen…
