Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
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.
ShapeX - Collage - Free Shape-Collage Generator! – (v1.1) Save Example Images & New Examples !
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Photovisi - Photovisi is a free and easy to use online tool to create photo collages.