An optical image system includes, in order from an object side to an image side, a first lens element with positive refractive power and having a convex object-side surface, a second lens element with positive refractive power, a third lens element with negative refractive power and having a concave object-side surface and a convex image-side surface, and a fourth lens element with refractive power and having a concave image-side surface. By such an arrangement, the total track length and photosensitivity of the image capturing lens assembly can be effectively reduced while retaining a high image quality.