Arsenic async API : session.get_screenshot() to capture image in particular location

Question

I have been trying to take screenshot of captcha based on ID from URL https://elegalix.allahabadhighcourt.in/elegalix/WebStartCaseSearch.do in arsenic async web driver.

async with get_session(services.Chromedriver(), self.browser) as sesssion:
     await session.get("https://elegalix.allahabadhighcourt.in/elegalix/WebStartCaseSearch.do")
     #Below gives <_io.BytesIO object at 0x7f6625119f68>. How to retrieve captcha image from this object
     captcha_image = session.get_screenshot()

But as per API documentation of Arsenic https://arsenic.readthedocs.io/en/latest/reference/session.html,

get_screenshot() : Coroutine to take a screenshot of the top-level browsing context’s viewport. Return type: io.BytesIO

we can only take entire page of screenshot, I would like to know any way to take particular image element ID and store it as base64 as we do it in Selenium below.

captcha_image = driver.find_element_by_id(
                'captcha_image'
            ).screenshot_as_base64