- Your dishwasher drain line goes to an airgap, mounted on the sink. make sure its free of garbage, leftovers, etc.
- then it continues to the garbage disposer. Make sure this line is free too.
You have to remember that the dishwasher drain goes from floor level up to countertop level, and you can expect some water to remain at the bottom of the unit, after it stops. It looks to me that your dishwasher is OK.
It only drains to about three inches above the trap under the sink and I may be wrong but I think they have a check valve of sorts