I have a problem getting verification code from server

Question

<img src="{:captcha_src()}" This method is used by default at the beginning

It can't be seen clearly. When changing one, the second method is used "/captcha? id=" ts

Do these two methods call the captcha class method corresponding to the server?

If so, why is the first one preceded by :captcha_src( )

The second method is /captcha

There is another problem. I checked the source code and only the captcha_src() name and captcha() method name

The second method What is used is this "/captcha? id=" ts Which method will the server be called at this time?