Select the desired image here by clicking on Edit. With Delete, an
image can be removed again; with Edit alternative text, you can enter text that will
be shown instead of the symbol on end devices that are incapable of
showing images.
If Show image in original size is selected, the chosen image
will be displayed at its original size. If that setting is not
selected, the image will be displayed at 16 x 16 pixels for desktop
screens, and 32x32 pixels on mobile devices.
The setting Filter is active causes the image
button, which is selected here, to be active when the page is loaded
and to filter the results.
Edit. With 
Delete, an
image can be removed again; with 
Edit alternative text, you can enter text that will
be shown instead of the symbol on end devices that are incapable of
showing images.