ImagePool fix

[zhufeida]

class ImagePool(object): 
    def __init__(self, maxsize=50):
        self.maxsize = maxsize
        self.num_img = 0
        self.images = []
    def __call__(self, image):
        if self.maxsize == 0:
            return image
        if self.num_img < self.maxsize:
            self.images.append(image)
            self.num_img=self.num_img+1  //It seems you forgot this line
            return image
        if np.random.rand() > 0.5:
            idx = int(np.random.rand()*self.maxsize)
            tmp = copy.copy(self.images[idx])
            self.images[idx] = image
            return tmp
        else:
            return image

[xiaowei-hu]

Thank you for your help. I have fixed the bug in the latest commit.