Image Field not able to change it to readonly?

Hi 

Below is my full code. 

I have a button for user to click and the code should compress the fields including all the images. 

-code-

var cMsg = "Clicking on this button will render all information in this page to be locked. ";
cMsg += "\n\nPlease confirm all the information provided is final. Are you ready to proceed?";

var nRtn = app.alert(cMsg,2,2,"Question Alert Box");
if(nRtn == 3)
{
}
else if(nRtn == 4)
{ this.getField("Counterparty_pg1").readonly = true;
this.getField("Free1").readonly = true;
this.getField("Free2").readonly = true;
this.getField("Beneficiary").readonly = true;
this.getField("Relationship").readonly = true;
this.getField("Relationship2").readonly = true;
this.getField("Explanation").readonly = true;
this.getField("Name").readonly = true;
this.getField("Address").readonly = true;
this.getField("Country").readonly = true;
this.getField("PIC").readonly = true;
this.getField("PIC Phone").readonly = true;
this.getField("Bank name").readonly = true;
this.getField("Bank Address").readonly = true;
this.getField("Bank Country").readonly = true;
this.getField("Bank Swift").readonly = true;
this.getField("Beneficiary1").readonly = true;
this.getField("Account Currency").readonly = true;
this.getField("IBAN").readonly = true;
this.getField("Corr Bank Name").readonly = true;
this.getField("Corr Bank Swift").readonly = true;
this.getField("Signature circle_pg1").readonly = true;
this.getField("Signatory Name_pg1").readonly = true;
this.getField("Signatory Designation_pg1").readonly = true;
this.getField("Letterhead1_af_image").readonly = true;

}

-ends code-

Pls advise how to amend?

Thanks,

Yixiang

Hihi, 

User open the file using adobe reader or DC. User can just click on the image field area and the pop up dialog box will appear to allow user to add new image or edit it. 

My case: the user fills up the image and text on all the field and upon clicking the "save" button, the file will compress or flatten such that no text or image can be edited again. I am having issue with the image. how should i do it?