Hi,
I would like my users to be able to submit an item only by filling in the required extra fields and upload a photo (like if it was a form).
No text, no editor, no tags.
Is that possible?

Yes of course provided that the title and category are present and we talking about the front-end submission form.

You can override the itemform.php file and remove/ hide the elements you want to.
More on overrides can be found here: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates