1. A method of estimating a blood pressure based on a video of a user, comprising: obtaining, by camera, an image including a skin of the user; determining, by a computer device, a skin region, in which at least one portion of the skin is displayed, from the image, and storing a specific value generated from color data of a designated color model for each of two different portions of the skin; estimating, by the computer device, a pulse wave signal based on a change in specific value of color data for each of the two different portions of the skin; estimating, by the computer device, a pulse-wave transit time (PTT) based on a time difference between local extrema of the pulse wave signals from the two different portions of skin; and estimating, by the computer device, the blood pressure using the PTT.