Documentation:
Image Box

Position

Here you can set the position of the title and caption text area.

Text / Image Ratio

Here you can set the width of the text area in relation to the image.

Note: The effect of this setting can only be seen when the text area is positioned to the left or right of the image.

Text / Image Gap

Here you can set the size of the gap between the text area and image.

Title / Caption Gap

Here you can set the size of the gap between the title and caption.

See here for an example.