Let’s break down some options:
1. If your logo and photo are large, colorful, and fairly detailed then you might find it best to use a single solid color as your background. Try using one of your brand/organization colors to compliment your logo. To take that a step further, using the same brand color you can create a gradient (going from light to dark) across the background to add a bit more visual appeal over the solid color.
2. Another popular option is to use a photo of your facility. This can promote a sense a pride as well as act as an additional layer of security by tying the badge to your specific location.
3. You could also try using a larger, watermarked version of your logo spread across the entire background, further re-enforcing your brand.
4. Or you could go the more abstract route; using various lines, shapes and forms to create your own unique visual design. Experiment, try many different things, but most importantly of all - have fun!
Using the background is an effective way to make your ID look professional and pretty cool but remember, less is more. Going overboard can take away from the cards performance but adding a minimal design and including brand colors can make your ID cards something to be proud of.
If you are just getting started in designing your ID card checkout the into to this series: How to Create Effective ID Badges: Intro. If you are interested in seeing some sample ID's to help with the brainstorming process check out these sample ID cards.