void identify_rgbimage(const RgbImage *base, Rect portion,
char result[MAXIMGIDENT], const char *what);
RgbImage *alloc_rgb_image(int w, int h);
void identify_rgbimage(const RgbImage *base, Rect portion,
char result[MAXIMGIDENT], const char *what);
RgbImage *alloc_rgb_image(int w, int h);