Kusubooru is displaying only safe rated images to visitors without an account. Thus you need to make sure that only "truly safe" images are rated as safe.
Safe Images (The Golden Rule)
Rate an image as safe if and only if you are 100% sure that you can comfortably view that image with your family and friends and colleagues and in public without the slightest regret.
Rate an image as questionable if there are certain elements in that image that would make you feel uncomfortable if you were viewing it in public or with your family or friends or colleagues.
Rate an image as explicit if contains elements of adult content such as nudity, private parts, breasts, penetration, sexual tickling and other explicit sexual activities.
Tickling as well as other fetishes (feet, armpits etc) should not be rated as safe unless the image is drawn in such a way that it satisfies the Golden Rule.
Be mindful of pictures that contain a combination of tickling, other fetishes, underage characters, minor bondage and exposed body parts. Prefer the questionable rating.
If an image fails to satisfy the Golden Rule and does not contain explicit content then use the questionable rating.
If an image is already rated, think twice before you change it's rating.
Do not give the safe rating easily.
If truly in doubt, you can always leave an image as unrated.
Always remember the Golden Rule when rating images.
Images rated as safe despite portraying tickling: >>521, >>1401
Images rated as questionable because they portray tickling, minor bondage, underage characters, partial nudity etc: >>600, >>800