How can I force Wordpress post format?

Hi, I have an urgent request.

A theme I have for a client makes use of the Wordpress's post formats. My client's posts are in the Standard format. However, the format we have decided to go with is the Image format.

One big huge problem though, her previous post are not showing in standard format. The initial post link in the blogroll shows, but the single page post does not show it's content when visited. When I set that post to Image, everything shows as it should. I'm not sure of why, and even the new Wordpress 3.6. settings is set to Image format for default, but makes no difference.

We haven't went through all her blogs posts yet to make them the Image format as she wanted to rush the project launch.

Is there a quick function I can add to make all her posts force the Image format and ignore the other post formats?

Kind regards,