You have acquired a microscope image from the sample which is displayed in the CAD model.
Load the Reference Image. Usually this will be the CAD image or file.
Below the image area you will see an image browser. Make sure that the image (microscope image) is already loaded and displayed in the browser.
Double-click (or Drag & Drop) the microscope image in the image browser.
The image will be loaded to the Image List and automatically displayed as overlay image in the image area.
Adapt the microscope image to fit the reference image. You can adapt (turning, resizing, dragging) the image by clicking on it (image frame with several handles will be visible).
When you are satisfied with the positioning click Create Overlay Image.
The overlay image will be created and is available in the image list (right side). Do not forget to save the image via right-click / Save As... function.