How to selective caching of images?

How-to
1

I want to cache images selectively，With some letters on the cache。
lv_img_cache_open（），This function is used to find whether the image has been cached，which function is cache images？thanks

2

cache images function is in lv_img_cache_open(),I just saw this…
/The image is not cached then cache it now/
if(cached_src == NULL) {