final App app = StructrApp.getInstance(securityContext);
try {
originalImage.setProperty(File.checksum, newChecksum);
Thumbnail thumbnailData = ImageHelper.createThumbnail(originalImage, maxWidth, maxHeight, cropToFit);
if (thumbnailData != null) {
Integer tnWidth = thumbnailData.getWidth();
Integer tnHeight = thumbnailData.getHeight();
byte[] data = null;
try {
data = thumbnailData.getBytes();
final String thumbnailName = originalImage.getName() + "_thumb_" + tnWidth + "x" + tnHeight;
// create thumbnail node
thumbnail = ImageHelper.createImage(securityContext, data, "image/" + Thumbnail.FORMAT, Image.class, thumbnailName, true);