GIMP is a Must or it might be a must. For those using Linux for example. BTW new version GIMP 2.10 was released but I had it's Debian version on my disk for too short.
"A Must" for many amateur photographers and their photos, especially made with old, used Pentax cameras (I think so) or other brands' family toy cameras, true 8Mp old timers like
Canon PowerShots A590 IS or
Panasonic Lumix DMC-LS80
GIMP was used to correct the image. Unsharp option was applied before scaling down and after. Quality was set to 85 as it's the best for all websites, so for PentaxForums as well. It represents the best ratio quality verses file size. There was no need to use other options. The image made with the aforementioned Panasonic was good from conception.
Then I cropped it to get better composition.