Just saw that v1.7.2 has no way to determine a size of a blob.
If the blob content is saved in the database it would be:
// get size of image
$blobsize = qa_db_read_one_value(
qa_db_query_sub('SELECT OCTET_LENGTH(content) FROM `^blobs`
WHERE blobid=# LIMIT 1', $blobrow['blobid']),
If the blob content is NULL and the file system is used it would be:
$blobsize = filesize( qa_get_blob_filename($blobrow['blobid'], $blobrow['format']) );
Hope that helps.