Collective policy is fairly open and there are only a small number of topics which are banned. They are as follows:
Underaged Content - Any persons or characters that are under 18 years of age are not acceptable. This includes anime characters as well. If you do not know the character's age, then don't post the image please! Also, any actresses who have "just turned 18" will be removed. Just because they are 18 now does not mean the image you are using is. Wait until they are at least 21 years of age before using them as source material. In short, if they look to be under 18 then don't post the image here.
Private Images - Any images posted of a personal nature, such as reported self images or those of others, which cannot be proven to the Admin to be posted with the permission of the person in the image will be removed. Proof will be provided in a means that the Admin will communicate to the image poster. If the image can be widely found on the internet, then it is fair game. If it cannot, then the image will be removed. Amateur porn site images are acceptable as they are not private images.
Sailor Moon and Disney Princesses - The entire series and characters are banned from the Collective. Cosplayers over 18 years of age can be posted, but any drawn images from the series are not acceptable.
Hate and Similar Themes - Themes such as racial hate, bestiality, death and other obviously unacceptable themes will be removed at the discretion of the Admin. Extremely distasteful subject matter, for example scat or similar themes, will be removed should it appear. As well, images which are reported to the Admin which are unacceptable will be removed.
Reposting Deleted Images: If a User deletes their work from the Collective, it is not permissible to repost their work. Images are posted on the Collective, or removed by the User who did so and has the right to do so. No one should assume they have the right to repost anything without permission.
Beyond these banned subjects, we ask that Collective Members please refrain from flaming, trolling or similar actions. Those that do so will be warned and then banned if they continue to do so.
Additionally, the following is specific to an issue that has occurred on the Collective in the past:
Respecting Other Members: In the past there have been instances of toxic Dommes and Doms posting advertisements on the Collective or having their followers do so. As well, there have been instances of submissives being contacted by such individuals and pressed into giving out information or other more disturbing events occurring. TO BE CLEAR: Any such advertisements will be removed. Any actions found to endanger any member of the Collective will result in action by the Admin. It is expected that Collective members will respect each other and that respect be returned from other members.
One additional point as Tumblr has gone away:
Unmanipped images should not be posted in the Gallery. If you want to post such an image, please add your story to the image and then post it. We cannot support the posting of images that have not been modified in some way. Putting text in a block beside the image is the minimum needed for posting to the Collective Gallery.