What Tibor95 means is that there is a free toolbox out there called ImageMagick that can do very many simple editing operations on images, and these operations can be combined. For instance, this:
convert "$f" -modulate 100,120 -geometry 3000 -sharpen 0x1.0 -quality 85 "$dir/$(basename "$f" .JPG).jpg"
Takes a picture, augments saturation, resizes it so that it becomes 3000px on it largest side (the other side being resized accordingly), and sharpens the result, and save it as a JPG with quality 85 (this is a Linux shell script, but you can do equivalent things in Windows).
The two main commands in that toolbox are "convert" (as above) that acts on one image, and "compose" that takes several input images to make one image.
Unless you are using very specific plugins, most uses of Gimp in batch can be replaced by scripts around ImageMagick (that will often run circles around Gimp).