image: move border calculation to calculateSizes().
image: move border calculation to calculateSizes().

ZiRo-/captcha,thomasmodeneis/captcha,oblank/captcha,zj8487/captcha,dchest/captcha,ZiRo-/captcha,eleme/fork_captcha,gotomypc/captcha,msn217/captcha,rainyear/captcha,kaz8/go-captcha