Ah, okay - you're using 1.3.5sr2, I assume? That version does indeed use the topic id in the ALT attribute for the topic image.
1.3.6rc1, however, uses the topic name for both the ALT and the TITLE attribute.
To change that, you would have to add another SQL query in COM_article(). You could get that code from 1.3.6rc1, if needed.
bye, Dirk