Google-sheets – Send email notification when a data in column matches a certain value

As Rubén pointed out, the format of sendEmail method is different: the last parameter is an object of options such as {attachments: ...}.

Also, images inserted in a spreadsheet via "insert image" are not associated with any cell in a sheet, they are just floating over the sheet. This makes them unsuitable for your purpose of matching images to recipients listed in the sheet.

Images via a URL

A way to associate images with cells is to use =image(url) formula, which requires the image to be accessible somewhere. I suggest the following approach: put the URL itself in the column for attachment, say D, and =image(D2) command elsewhere, just to have a preview of the image. Then you can obtain the image as a blob with

var image = UrlFetchApp.fetch(row[3]).getBlob()

and send it via

MailApp.sendEmail(emailAddress, subject, message, {attachments: [image]});

The full script is as follows:

function emailImage(){
  var EMAIL_SENT = "EMAIL_SENT";
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2;  // First row of data to process
  var numRows = 20;   // Number of rows to process
  var data = sheet.getRange(startRow, 1, numRows, 20).getValues();
  for (var i = 0; i < data.length; ++i) {
    var row = data[i];
    var emailAddress = row[0];  // First column
    var subject = row[1];       // Second column
    var message = row[2];       // Third column
    var image = UrlFetchApp.fetch(row[3]).getBlob();   // Fourth column
    var emailSent = row[4];     // Fifth column
    if (emailSent != EMAIL_SENT) {  // Prevents sending duplicates
      MailApp.sendEmail(emailAddress, subject, message, {attachments: [image]});
      sheet.getRange(startRow + i, 5).setValue(EMAIL_SENT);
      // Make sure the cell is updated right away in case the script is interrupted
      SpreadsheetApp.flush();
    }
  }
}

Images on Google Drive

If the images are stored in Google Drive, they can be accessed by file Id (the long alphanumerical part of their URL). Put the Ids in column D and replace the line with var image = by

 var image = DriveApp.getFileById(row[3]).getBlob();

if (value >= "B2") ...

That's just comparing value to the string "B2". You wanted to compare to the content of the cell B2. That is,

if (value >= sheet.getRange("B2").getValue())  ...