AWS Lambda : Serverless Image HandlerCustom resource

[Galniyaz]

Hello.
I am new to the topic of Serverless Image Handler on AWS.
I have a question about the ready-made solution serverless-image-handler .
When importing it, 2 lambda functions are created and one of them with the description Serverless Image Handler (v6.2.5): Custom resource.
Question: What is this function used for? I see that in Monitoring tools there is no data on the operation of this function.
I didn't find any answers in the documentation
Thank you