Coding is case sensitive
Python and JavaScript are both case sensitive languages. The commands you write in code components must be of the correct case, and the cases of the names of your components and variables must match. For example, you could have three distinct variables called item, Item, and ITEM (don’t do this).
In addition, when running online you also need to use the correct case for your filenames. Locally you can have item.png in your spreadsheet and your experiment will successfully display item.PNG. Online, however, this will fail so you will need to either change the capitalisations of the file names in your spreadsheet/experiment or change the file names themselves.