Resize, convert, or watermark many images at once – GIMP 3 with BIMP, Script-Fu batch mode, and the faster ImageMagick mogrify one-liners.
Batch Edit Images and Export Them Separately (GIMP 3 + ImageMagick)
Resize, convert, or watermark many images at once – GIMP 3 with BIMP, Script-Fu batch mode, and the faster ImageMagick mogrify one-liners.