Well by looking at them will only give you clue about the possible soot but you actually need to get them pattern tested. They use ANSU machine and test flow and CC delivered per selected time. If one or more are out of cone shaped pattern or are delivering less cc fuel than others then this means it needs service.
For proper testing you need to know the specs of injector at hand and their capacity. then you can be sure if they are within specs.
and @fahad.ayub No, washing them with carb cleaner or petrol is not a guarantee solution they need ultrasonic bath.
If injector is stick open you will face rich condition where as close stuck will cause a misfire. They just make car smooth dont expect wonders from injector cleaning. Yes it improves response and drive.
Get them cleaned anyway if your ride is above 100K
