Plugin to allow image uploads for guests

I am creating a very simple website for my sister, she’s getting married tomorrow!

I want to allow all the guests to send their photos via file upload to the website, perhaps using wordpress and a plugin.

I imagine 99% of all users will be doing this via their mobile phone.

I’d like users to not have to register, but be able to allow multiple uploads in one go.

Is there a free plugin out there that does this already? I have searched and haven’t yet found one that does what I’d like. “WordPress File Upload” is ok, but doesn’t allow multiple file uploads in one go.