It looks like a gourd to me.

Here is a link that might be useful: Autumn Wings

It is definitely an ornamental gourd, and a very beautiful one if I do say so myself. Was that picture taken this year? I wish I had gourds already mine are still seedlings.

Definitely. I grew lots of them (same size, color pattern and other types as well) last year. For this year, mine are about to flower.

My only gourd plant of this type is also voluntary, from last year's broken and rejects. I pulled out so many of them and kept just one plant.
The type shown, if let to mature on vine, can get pretty thick and hard. I have made several salt/prpper shakers from them. You have to treat them either with chlorine solution or vinegar to kill the molds on them and prevent possible rotting.