image field fdf data getting truncated in iis

Designed an AcroForm with a Image Field where this form is used by several users to submit their data which is saved in Database

writte the below code to submit the form

var aSubmitFields = new Array("Image1_af_image");
this.submitForm({
cURL: "http://localhost/sitenname/somepage.aspx"
,aFields: aSubmitFields
,cSubmitAs: "FDF" 
});

attached attachment for reference