Detect Base 64 encoding in images
var base64Matcher = new RegExp("^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$");
// ...
if (base64Matcher.test(someString)) {
// It's likely base64 encoded.
} else {
// It's definitely not base64 encoded.
}