Ristretto - grey bars

[Piscium]

Gray bars with a curved shape appear while displaying some images,
depending on size or some other unknown factor. Is this a bug or a
feature? Please see this picture:
https://drive.google.com/file/d/1o9cOxLkBn4J2zc6q1VtHOGqFMxzRC1L-/view?usp=sharing

I am using Ristretto 0.11.0 in Arch with the proprietary Nvidia driver
and Openbox WM. Other picture viewers don't have this problem.

P. S. What is the best site to share a picture with a short expiration
period? Not too happy to share from my google drive account (as
above), but don't want to put in a site that stores images forever or
needs registration.