It is taken from EXIF (or other metadata) section of the photo.
I suppose there is some binary information in the image, so server when tried to use it just marks as ‘binary comment’ and writes it into the observation.
If you look to https://www.inaturalist.org/photos/151628132, tou will see “binary comment” as comment of the photo.
Addition information: This happens to me when I post-process my images in GIMP or another software. I believe there is an option to turn off the comment.