You could try the gmic plugin from http://www.gmic.eu If using Gimp 2.8 get the correct version and read the pop up explanation of possible installation issues. eg. https://i.imgur.com/J14oh2w.jpg No such problem with Gimp 2.10
Looks like this: https://i.imgur.com/yHHqNkC.jpg play around with the slider settings
There are others, this one for example creates an anmation https://www.deviantart.com/fence-post/ar...-144814233
Another way is using a brush https://www.deviantart.com/aoarchangel/a...-147509615 these are a pair of animated brushes (the brush varies slightly as you paint), vary the brush size, paint in the image. https://i.imgur.com/HSnQFVm.jpg
Looks like this: https://i.imgur.com/yHHqNkC.jpg play around with the slider settings
There are others, this one for example creates an anmation https://www.deviantart.com/fence-post/ar...-144814233
Another way is using a brush https://www.deviantart.com/aoarchangel/a...-147509615 these are a pair of animated brushes (the brush varies slightly as you paint), vary the brush size, paint in the image. https://i.imgur.com/HSnQFVm.jpg