Hi Anh,
Thank you for the feedback! In the meantime, I implemented a solution to automatically resize the original images after uploading if they are too large using the wp_handle_upload filter. That works and I do not need the functionality to stop uploading. It is probably a good practice not to delete images anyway, you never know what other plugins or themes expect in the Media Library. So this thread can be closed as far as I am concerned.
However, I will open another thread for the functionality of propagating an error about exceeding the max image size limit when trying to upload a file and displaying the error on the GUI in the plupload_image field. Perhaps the way to do that is to set $file['error'] in the same wp_handle_upload_prefilter as in my earlier example in this thread. Perhaps there is a better way to do it. In any case, thanks again for your feedback here!
