which images are youi talking about? As far as I knew they were all inserted using the CMS apart from the home page which uses code to either automatically show the most popular and a selected sale item or if none is available a default image - either shoes of wheel trims (cant work out the logic).
That hard code is in index.php on line 197 and 231 - you can of course change these for whatever you want remembering that they are test items.
As to loosing content are you talking about the stock content ? if so thats stored in the database. So either the database became corrupt or it was over written or as sometimes happens it's the law of SOD