This panel contains a label, identifying the image that is currently selected.
This label is usually set to the original file name the image was loaded from. However it can indicate other sources, such the original source being pasted via the clipboard.
The 'Maintain aspect ratio' check box controls the behavior that resizing this image overlay will have inside the project viewer.
When this checkbox is un-ticked you can freely drag each side of your image overlay to the size you require. However while ticked, the aspect ratio of the originally loaded image will be used to constrain resizing.
Rotate, Flip, Raise and Lower
The rotate left, rotate right, raise, and lower buttons will behave similarly to those in the 'Overlay menu'. The flip horizontal, flip vertical buttons will flip the selected image overlay accordingly.
See: Menu reference