copy file only if file size is different with wget paying no attention to timestamp

Question

wget -N http://host/path/file.jpg will retrieve the file if the file exists at target but either file size or its timestamp has altered.

My problem is that the source server alters timestamps but the file is the same, and I do not want to download files that have not been altered.

So if there would be a way to retrieve a file if the file name is the same but the file size is different and not to care about the timestamp at all?