The property AutoResizeChildren is 'on' by default, so it is 'on' in the 2 panels of the app.
However, AutoResizeChildren doesn't resize the images. There are cases where it makes sense to resize the images, but others where it doesn't (e.g. if the image is used as a logo), so the choice was to not resize images.
(If you place the images in a standard app, you will see that the images also don't get resized)
One way to make the images resize as described is to place a GridLayout in the right panel, and place the images in the grid.
By default, the rows and columns are all sized to be '1x', so they will share the available space equally.
When the panel is resized, the images will be scaled up and down accordingly.