How to upload a blob (image) into a google sheet using google sheet api v 4

I have a blob data. I would like to upload this to a cell in google sheet using google sheet API v4.

I have looked at the documentation here. https://developers.google.com/sheets/api/guides/values

I have also looked at SO questions here. Insert image into Google Sheets cell using Google Sheets API

result = service.spreadsheets().values().update(
spreadsheetId=spreadsheet_id, range=range_name,
valueInputOption=value_input_option, body=body).execute()

I am not seeing any service described to insert the blob as the image. Please help.

After suggestions below, we implemented the Webapp from here - Insert image into Google Sheets cell using Google Sheets API

This is how we are calling the web app from our python code

        dropoff_signature = "ZGF0YT <clip > WVhSaA=="
        web_app_url     = "https://script.google.com/macros/s/A < clip > y/exec"        
        image_data  = "data:image/png;base64," + dropoff_signature
        data_to_post = {            
            'spreadsheetid' : spreadsheet_Id, 
            'sheetname' : 'Sheet1',     
            'imageurl'  : image_data,              
            'column'    : 5, 
            'row'       : 5             
            }
        encoded_data = urllib.urlencode(data_to_post)
        # Send encoded data to application-2
        url_result = urlfetch.fetch(web_app_url, encoded_data, method='POST')           

We are seeing the following error in our Webapp.

result : 200 content : {"status":"error","defaultMessage":"Error retrieving image from URL or bad URL: data:image/png;base64, <clip> ","name":"Exception","fileName":"Code (Insert image into spreadsheet)","lineNumber":42,"stack":"\tat Code (Insert image into spreadsheet):42 (doPost)\n"}}

Can you please help?

Made this change. Still getting the bad URL error.

dropoff_signature = "ZGF0YTpp<clip>WVhSaA=="
        web_app_url     = "https://script.google.com/macros/s/A<clip>y/exec"        
        image_data  = "data:image/png;base64," + dropoff_signature
        data_to_post = {            
            'spreadsheetid' : spreadsheet_Id, 
            'sheetname' : 'Sheet1',     
            'imageurl'  : image_data,              
            'column'    : 5, 
            'row'       : 5             
            }
        # encoded_data = urllib.urlencode(data_to_post)
        # Send encoded data to application-2
        # url_result = urlfetch.fetch(web_app_url, encoded_data, method='POST')         
        url_result = urlfetch.fetch(url=web_app_url, payload=json.dumps(data_to_post), method='POST', headers={'Content-type': 'application/json'})



result : 200 content : {"status":"error","defaultMessage":"Error retrieving 
image from URL or bad URL: 
data:image/png;base64,Z<clip>A==","error": 
{"message":"Error retrieving image from URL or bad URL: data:image/png;base64,Z<clip>A==","name":"Exception","fileName":"Code (Insert image into spreadsheet)","lineNumber":42,"stack":"\tat Code (Insert image into spreadsheet):42 (doPost)\n"}}

Here is the Webapp that we are using.

function doGet(e) {
  return ContentService.createTextOutput("Authorization: Bearer " + 
  ScriptApp.getOAuthToken())
}

//
// Example curl command to insert an image:
// 
// curl -L -d '{ "spreadsheetid": "1xNDWJXOekpBBV2hPseQwCRR8Qs4LcLOcSLDadVqDA0E","sheetname": "Sheet1", "imageurl": "https://www.google.com/images/srpr/logo3w.png", "column": 1, "row": 1 }' \
// -H "Authorization: Bearer <INSERT TOKEN RETURNED FROM GET HERE>" \
// -H 'Content-Type: application/json' \
// https://script.google.com/a/tillerhq.com/macros/s/AKfycbzjFgIrgCfZTvOHImuX54G90VuAgmyfz2cmaKjrsNFrTzcLpNk0/exec
//

var REQUIRED_PARAMS = [
  'spreadsheetid', // example: "1xNDWJXOekpBBV2hPseQwCRR8Qs4LcLOcSLDadVqDA0E"
  'sheetname',     // Case-sensitive; example: "Sheet1"
  'imageurl',      // Can be an url such as "https://www.google.com/images/srpr/logo3w.png"
                   // or alternately "data:image/png;base64,iVBOR...<snip>...gg=="
  'column', // 1-based (i.e. top left corner is column 1)
  'row'     // 1-based (i.e. top left corner is row 1)
];

function doPost(e) {

  var result = {
    status: "ok",
    defaultMessage: "Image inserted."
  }

  try {
    var params = (e.postData && e.postData.type == "application/x-www-form-urlencoded") ? e.parameter
    : (e.postData && e.postData.type == "application/json") ? JSON.parse(e.postData.contents)
    : undefined;


    if (!params) throw new Error('Unsupported content-type, must be either application/x-www-form-urlencoded or application/json.');

    REQUIRED_PARAMS.forEach(function(requiredParam) {
      if (!params[requiredParam]) throw new Error('Missing required parameter ' + requiredParam);
    });

    SpreadsheetApp.openById(params.spreadsheetid).getSheetByName(params.sheetname).insertImage(params.imageurl, params.column, params.row);  

  } catch(e) {

    console.error(e); 

    result.status = "error";
    result.error = e;
    result.defaultMessage = e.message;

  }  

  return ContentService.createTextOutput(JSON.stringify(result))
    .setMimeType(ContentService.MimeType.JSON)  
}