PhotoPenguin App - PhotoPenguin is a completely free batch photo editor with support for cropping, resizing, adding watermarks, and converting photos to other formats. It works on the user's device, using the capabilities of modern browsers.

GIMP - GIMP is a multiplatform photo manipulation tool.

ImBatch - ImBatch is a batch image processor with a nice graphical user interface.

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.

Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats

MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.