Air Filtration : Improperly Sized Filter
Your central air system is equipped with an air filter. It is typically within the return air duct, before the blower. (Although in some homes, the filter can also be behind a return air grating within a wall in the living space to make it more accessible). 'Return' air is pulled from the living space of the home, through the filter, and then pushed across the AC coil to be cooled (or pushed across a heat exchanger to be heated) before it becomes 'supply' air blown back into the home's living space.
The air filter pictured above is improper, due to it being an incorrect size and the compartment being unsealed. In the picture, return air should be pulled down the silver ductwork on the right, pass through the air filter, and then into the blower compartment on the bottom left, before it is pushed across the AC coil and up into the home as 'supply' air.
In the condition above, air is not being pulled from the home's return duct, but rather is being pulled from the gap at the filter before being supplied into the living space. Air is therefore not being filtered, and this will cause dirt and debris to collect on the blower and AC coils, reducing efficiency. Possibly worse, return air is not being pulled from the living space, preventing the air in the living space from cycling back to the unit - an even bigger inefficiency. Lastly, for this particular unit located in basement, the improper filters are allowing the basement air to be pulled into the blower and supplied into the living space. Depending on the basement air quality, this may not be desirable.
This unit will require a cleaning (to remove all the debris that bypassed the filter) and repair (a properly size filter installed and the filter compartment lid installed) to allow it to operate efficiently and prolong the life of the unit.
Once repaired, the filter should be replaced at regular intervals based on the manufacturer's recommendation. Clean air filters will help keep the unit running efficiently and help reduce allergens in the home.