A system for verifying a video call number entry in a directory service, the directory service comprising a client interface connected to a computer network, an application service and a video calling service, the client interface being configured to: receive a video call number from a user for entry in the directory service, and submit the received video call number to the application service to initiate verification of the video call number, receive a registration challenge response from a user, and submit the received registration challenge response to the application service to validate the registration challenge response; the application service being configured to: receive the video call number from the client interface for verification, generate a registration challenge, store the registration challenge and the video call number in a session, and submit the registration challenge and the video call number to the video calling service, receive the registration challenge response from the client interface, load registration challenge from the session, and upon finding a positive match between the registration challenge and the registration challenge response, updating the directory service indicating the video call number being valid; and the video calling service being configured to: receive the video call number and the registration challenge from the application service, initiate a video call session to the video call number, and upon successful initiation of the video call session, presenting the registration challenge to the user over the video call session, wherein the system further comprises an encoding service configured to: generate a one image file based on the registration challenge, and generate a video sequence file by creating multiple copies of the image file and encode the multiple copies of the image file into a video format, wherein video calling service is further configured to present the registration challenge to the user over the video call session by transmitting the video sequence file; and wherein the client interface is in web page format and includes listings of video call numbers uploaded into the directory service, search functions to find video call numbers in the directory service and the possibility to upload video call numbers into the directory service. receive a video call number from a user for entry in the directory service, and submit the received video call number to the application service to initiate verification of the video call number, receive a registration challenge response from a user, and submit the received registration challenge response to the application service to validate the registration challenge response; receive the video call number from the client interface for verification, generate a registration challenge, store the registration challenge and the video call number in a session, and submit the registration challenge and the video call number to the video calling service, receive the registration challenge response from the client interface, load registration challenge from the session, and upon finding a positive match between the registration challenge and the registration challenge response, updating the directory service indicating the video call number being valid; and receive the video call number and the registration challenge from the application service, initiate a video call session to the video call number, and upon successful initiation of the video call session, presenting the registration challenge to the user over the video call session, generate a one image file based on the registration challenge, and generate a video sequence file by creating multiple copies of the image file and encode the multiple copies of the image file into a video format, wherein video calling service is further configured to present the registration challenge to the user over the video call session by transmitting the video sequence file; and wherein the client interface is in web page format and includes listings of video call numbers uploaded into the directory service, search functions to find video call numbers in the directory service and the possibility to upload video call numbers into the directory service.