Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
Dibuja - Gtk based basic paint program like MSPaint or Paintbrush but for Linux
GIMP - GIMP is a multiplatform photo manipulation tool.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.