From FreeCAD Documentation
- To edit an Image Plane do one of the following:
- Double-click the Image Plane in the Tree view.
- Right-click the Image Plane in the Tree view and select Change image... from the context menu.
- If the Image Plane is not plane-parallel to the XY, XZ or YZ plane of the global coordinate system, it is realigned to be plane-parallel to the XY plane.
- The Image plane settings task panel opens.
- Optionally select the XY-Plane, XZ-Plane or YZ-Plane of the global coordinate system.
- Check Reverse direction to rotate the Image Plane 180°. The rotation axis depends on the selected plane. For the XY plane it is the global X axis. For the XZ and YZ plane it is the global Z axis.
- The Offset, X distance and Y distance are relative to the coordinate system of the Image Plane. A small negative offset can be useful when tracing the image with a sketch or Draft geometry.
- Optionally change the Transparency.
- Image size options:
- Scale by numerical input:
- Optionally uncheck Keep aspect ratio for unequal scaling.
- Enter a Width and/or Height.
- Scale by picking points:
- Press the Calibrate button.
- Pick two points inside the image.
- A dimension line is displayed.
- Enter the desired dimension.
- Press Enter or the Apply button.
- Press the OK button to confirm the changes and close the task panel.