Many Internet service providers and other online service providers are blocking their users from accessing web addresses about sexually explicit material. In addition , Internet providers may block the retrieval or uploading of child sexual abuse videos , images. This is how they use filtering and blocking technology. Now whatever is written in the web address about this will be filtered and blocked directly. This list is compiled and given to the police agency. Certain phrases such as "child sexual abuse" can be created through filtering and blocking. Where a specific image is already known to the police , hashing technology , photo DNA or digital fingerprints can be created. This hash can then be transferred to their database and system and it can be used to find out if any such image has already been uploaded or downloaded to their server.