This is usually an indication of low refridgerant level. Time for a service. To clear the airhandler coil of ice, turn the unit off an leave the fan running on manual until ice clears. You may get some cooling back until service arrives.

I had a situation on a Lennox system some years ago. Variable-speed ECM blower motor, it went wonky and was running backwards, thus no airflow.

It sounds like to me that you have no air flow, or bad air flow quality. You are going to want someone to come take a look at it. If it keeps freezing then you are not getting the right air flow. Perhaps you need it cleaned out.

By the look of the frost pattern on the coil, it's more than likely low on refrigerant or possibly a restricted expansion valve.

There are a variety of other reasons:

37 year HVAC veteran

Here is a link that might be useful: How to fix air conditioer that freezes up

Great link! I can't imagine it would be undersize ductwork, it just started freezing. Have you checked the filter? When was the last time you had the A/C unit serviced? Once a year is the trick. If you recently did they would have caught a clogged filter. I would call your local HVAC company and tell them what is going on. You don't want to do more damage to the unit.