How to set a featured image

I run a community news site where we allow the public to submit news to the site. We allow users to do this via a form created in TDOMF. We also allow user to submit an image with their news.

what i would like is when a user attaches an image to the post the image is set as the featured image automatically for thumbnails etc.

this is because when a register users submits news via the form (never going to wp backend) their post is not moderated so at present no thumbnails is attached to the image. This mean i have to login and edit ever post and set the image as featured, which is a pain when im getting 20-30 posts a day and is only going to increase.

Can anyone help??