I have managed to solve it ! Thanks anyway !
$(document).ready( function(){
var count = document.getElementsByClassName('respondCanvas').length;
var imageObj = new Image();
imageObj.src = "/frontEnd/images/coupons/back1.png";
var canvas = new Array();
var context = new Array();
for (var i=1;i<=count;i++) {
canvas[i] = document.getElementById("respondCanvas_"+i);
context[i] = canvas[i].getContext('2d');
}
imageObj.onload = function () {
for (var i=1;i<=count;i++) {
context[i].drawImage(imageObj, 0, 0);
}
};