|Today I discovered 'quickmask'. On bottom left corner of the picture area on GIMP there is so called 'quickmask' button. To use it first make sure you select all: 'Select > All'. Then just click that quickmask button. Now the picture should turn into reddish mask.
EDIT: For some reason the image does not always turn reddish when mask becomes applied. Do not let that bother but just continue to next stage.
|Next stage is to decide what you select, and for this you can use 'Blend tool' with different 'Gradients'. In this example I picked 'Radial Gradient' because I want to treat the edges differently than the center of the image. When you are done you get the reddish mask blending gradually from darker red to lighter.|
|Now all you need is to click the quickmask button again, and the mask turns into selection. Now make sure you get selected what you wanted. If just the border of circle flickers, then circle it is what you get. But if you choose 'Select > Invert', then it is the area between the circle and edges of the image.|
|Finally you can for example duplicate the layer, run 'Filters > Artistic > Photocopy…' for the edge part of the image, and then turn the overlapping layer to 'Soft light' layer mode. As a result you get nice white vignetting (edges are lighter than center of the image).|