You are reloading the image in the update function which is causing your delay:
circleImage.src = "images/Circle.png"; //re-draws image
All you have to do is drawImage without reloading the image:
ctx.drawImage(circleImage, circle.x, circle.y);
Here is an example of an image loader that loads all your images before execution begins:
var imageURLs=[]; // put the paths to your images here
var imagesOK=0;
var imgs=[];
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house1.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house2.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house3.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house4.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house5.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house6.jpg");
loadAllImages(start);
function loadAllImages(callback){
for (var i=0; i<imageURLs.length; i++) {
var img = new Image();
imgs.push(img);
img.onload = function(){
imagesOK++;
if (imagesOK>=imageURLs.length ) {
callback();
}
};
img.onerror=function(){alert("image load failed");}
img.crossOrigin="anonymous";
img.src = imageURLs[i];
}
}
function start(){
// all your images are fully loaded so begin your app
}