see the man page for errno
errno 33 is EDOM. you can usually find what that means by printing the output of
strerror, like so:
In this case, you would have gotten something like “Mathematics argument out of domain of function” as an output.
You will also get useful results from googling something like “errno 33”.
Anyway, if we take a look at the documentation for
vision_get_by_size, we can see that
EDOM signifies “size_id is greater than the number of available objects.” Since you’re requesting the zeroth object, this in turn means that there are no objects detected.