I am not sure whether I fully understand what you mean, although I’ll try my best.
[In JavaScript] to convert the base64 image to a JPG and save it with the student ID as the filename, you can add the following code to your Postman pre-request script:

// Retrieve the base64 image from the response
const base64Image = pm.response.body;

// Convert the base64 image to binary format
const binaryImage = atob(base64Image);

// Create a Blob object from the binary image data
const blob = new Blob([binaryImage], { type: "image/jpeg" });

// Create a file name using the student ID
const studentID = pm.variables.get("studentID");
const fileName = studentID + ".jpg";

// Save the image to disk
const fileReader = new FileReader();
fileReader.onload = function () {
  const imageDataUrl = fileReader.result;
  pm.sendRequest({
    url: "https://postman-echo.com/post",
    method: "POST",
    header: {
      "Content-Type": "application/json",
    },
    body: {
      mode: "raw",
      raw: JSON.stringify({
        image: imageDataUrl,
        fileName: fileName
      }),
    },
  }, function (err, res) {
    console.log(res);
  });
};
fileReader.readAsDataURL(blob);

I detail the code:

1. First, you retrieve the base64 image from the response using pm.response.body.

2. Then, convert the base64 image to binary format using atob().

3. Create a Blob object from the binary image data using the MIME type "image/jpeg".

4. Create a filename using the student ID, which is retrieved using pm.variables.get("studentID").

5. Then use a FileReader object to read the image data and convert it to a data URL using readAsDataURL(). Once the data URL is generated, we send a POST request to Postman Echo with the image data and filename as JSON in the request body.

Welcome to the community! Please, next time remember that your code should be directly written or pasted in Markdown, as above.

I hope it helps!