Failure to obey a police officers demands is illegal and is a crime if you're being given a lawful order by the police officer.
However if you're doing nothing illegal like say taking pictures from a public street etc and a police officer orders you to stop taking pictures and you fail to obey those orders then no it's not illegal.
The order that the police officer is giving you must be a lawful order or you must be suspected of or be committing a crime for the order that the officer is giving you to make it a crime to not obey the police.
If the police give you a lawful order and you fail to obey the officers orders then yes you can be arrested for failure to obey the officer.
Or if you go into a crime scene where an officer tells you not too and then gives you a warning to stay back and you don't obey then you can be arrested.