If you, for example, take out the mustard that you have tracked in your fridge, use it then put it back but at an angle the FridgeCam hasn’t seen before it will not recognise that it is there.
The app will notify you saying 'item not found' and give you two options, to add the item to your shopping list or to re-label and re-track.
If the item is still in the fridge, select re-label and re-track. The app will ask you to re-label by drawing a box around the item. When labelling, ensure that you are only labelling the item itself and do not have any of the background or other items in the box. If you have an item with clear packaging, such as a glass jar or bottle, draw a box around the label of the item.
This is teaching the FridgeCam what your items are and what they look like so they will be tracked with ease.