Removing dust specks: image 3
This image shows two objects in the sky area that might represent a distraction: a hair that was probably on the camera lens and a plane in the sky.
This raises an interesting ethical dilemma - whilst it seems right to remove the hair (as an object that was not part of the image), is it ethical to remove the plane that was at the time part of the image. My view is that the answer might depend on the circumstances and the use of the image. I generally think that image adjustments and corrections should be kept to the minimum; however, in some circumstances it might be necessary to make changes to the image.
The plane in this instance is not a permanent feature of the image: it would have been possible to wait for the plane to reach the edge of the image before taking the picture.
Pictures 7 and 8: Image 3 showing a hair on the lens and a plane

Lessons from the exercise:
1) Both clone stamp tool and healing tool are very useful for making adjustments to an image: they both are suitable for general retouching but have slightly different functions. For example, the healing brush is best to make smooth transitions of colour and luminosity.
2) It is important to view any image at 100% enlargement: not only you can spot the tiniest dust specks but also find other elements that might need correction (for example, lens flare).
3) A clone source function can be used to change the angle of cloning adjustments (clone source angle) and make upside down adjustments.
4) A healing brush can be changed to a different shape (e.g. an eclipse) to improve the blend.
5) It is possible to use a selection function to restrict the area that need to be adjusted.
6) Creating a duplicate layer for adjustments helps to protect the original image from unwanted and accidental changes.
Picture 9: Image 3 after the adjustments