Something like this (I uploaded an image file to the assets, then copied this over to the ASD, which is where your canvas image will be saved):
SCRIPT
(the script is bound to the spreadsheet)
function doPost(e) {
var ss = SpreadsheetApp.getActive();
var sh = ss.getSheetByName('Sheet1');
var data = Utilities.base64Decode(e.parameters.data);
var blob = Utilities.newBlob(data, e.parameters.mimetype, e.parameters.filename);
var fileID = DriveApp.getFolderById(e.parameters.folderId).createFile(blob).getId();
sh.appendRow(['=image("https://drive.google.com/uc?id=' + fileID + '")',fileID,e.parameters.filename[0]]);
return ContentService.createTextOutput("Image Uploaded: " + fileID);
}
BLOCKS
SCREEN
SHEET
