Disclosure: I am not a plumber but I called a plumber and am unsure about his plan of action to fix my problem. I am hoping to bounce some thoughts from you all here. I have a dishwasher that I do not use but that gets periodic standing water on the bottom, which stinks to high heaven. I have a farm sink, a disposal, and a high loop under the sink (the line that connects from disposal to dishwasher). The disposal is attached to the pipe in the wall with an accordion pipe (put in by previous owners). The plumber has told me that he is very sure that the issue is that the disposal sits too low and that the pipe is too high, causing the standing water issues because it's fighting gravity. His solution is to cut into my cabinet on the bottom and move the pipe connection to the ground, so that the pipe is not fighting gravity. I asked several times how this translates to the water in my dishwasher, but he couldn't explain, just kept saying that the water was fighting gravity. So, does this sound likely? Again, the hose that goes from the disposal to the dishwasher is in a high loop. He went straight to what I feel is the priciest of all solutions, that is, moving the pipe in the wall.
Looking at your picture, the disposal unit is improperly installed.
That white bendy straw looking flex pipe in the red circle is trapping water inside the disposal unit. The U shaped trap thing should drain strait into the waste pipe. What's happening is the flex pipe has raised the water line in the disposal unit. When you go to use your sink, the water is building up in that drop. This creates a little back pressure which the drain water has to overcome to fight past the water trapped in the flex pipe. Now have a look at that thinner white tube in the yellow circle entering into the disposal unit near the top. Notice how close it is to the high water line. That's the dishwasher drain line. Dishwashers have very simple plumbing to keep cost down so there is nothing keeping dirty sink water from overflowing into the dishwasher drain. This is where your standing water is coming from.
To fix this, a plumber would have to break that wall under the sink and lower that waste line eliminating the flex line and allowing the water to properly drain.