Automatically (this is the default value, for that reason the icon appears and disappears automatically in your environment). It will download ALL the image to client machines each time that a user open the requirement module.
On demand. With this option the user has the privilege to download ONLY the images that he/she wants, in this way the user will avoid to fill the temp folder memory with a lot of images.
Note: it is supposed that by default the setting is ''Automatically'' for all the users in your environment, so it means that all images were already downloaded in client machines, if the user(s) change the setting to ''On Demand'' they will still look the images because the images were downloaded in the machine, the only way to free the temp folder and delete the images for each client machine is deleting the td80 folder. after delete the td80 and selecting the option ''On Demand'' the user will be asked to download the required image's.