1. A method performed under control of a gesture-based game system, comprising: capturing, by an image capture unit, an image of a first player and an image of a second player; cropping, from the image of the first player and the image of the second player, a sub-image of at least part of the first player and a sub-image of at least part of the second player, respectively, in a first predetermined size and a second predetermined size based, respectively, at least in part on a preset position of the first player and a preset position of the second player; determining whether to adjust the sub-image of at least part of the first player and the sub-image of at least part of the second player; responsive to a determination to adjust the sub-image of at least part of the first player and the sub-image of at least a part of the second player, adjusting the sub-image of at least part of the first player and the sub-image of at least part of the second player; and merging the adjusted sub-image of at least part of the first player and the adjusted sub-image of at least part of the second player into an output image.