Starting point (doing it manually):.

After installing ImageMagick software sudo apt-get install imagemagick -y on a Debian-based distro, you can just use Terminal and your file manager.

Put  some image files in a folder. Open Terminal in that folder. Use 'magick convert' (which belongs to the ImageMagick software you installed) to resize, rename, and reformat the image files.

Example:

I placed 5 pngs into ~/Desktop/ImageFrom, altogether they weight 2mb. (I also have a folder desktop/ImageTo.) I open Terminal in ~/Desktop/ImageFrom and do mogrify:

mogrify -path ~/Desktop/ImageTo -format jpg -resize 1000x1000 *

This puts versions of all my pngs into my other folder, but they are now jpegs with the longest edge being 500px. They now weigh 225kb altogether.

Here ends the 'Starting point' part.

Blender for design. (AppImage)

Cura for slicing. (AppImage)

Crealty3d Ender 3.

Don't use newer Lubuntu, they suck (no internet).

After VirtualBox turned bad (everyone says it's much slower, and it can't even be installed on lots of OSs anymore), people are turning to Qemu, which is better anyway because it's FOSS.

It uses qcow2 files (currently), not .vdi files (which VirtualBox uses). You can 'migrate' .vdi files to become qcow files (use your old VirtualBox VMs in Qemu) but I haven't done that yet.

Install was not simple, but did work.

To make shared folders in the current Qemu, you have to go to Memory > checkmark on 'Enable shared memory', then click the button at the bottom of the list 'Add hardware', then go to 'File System' and here you keep driver as 'virtiofs' (this is just for LinuxHost-LinuxGuest, I've read, not for Windows). Set your source path (yes the actual path) to where you want your sharedFolder to be on your Host (create this folder also). For Target path, just put the NEWdIRECTORYnAME of the folder on your Guest (don't put the actual path to it, just the name). ... Now inside the GuestOS, do sudo mkdir path/to/your/NEWdIRECTORYnAME ... then (still inside the Guest, do sudo mount -t virtiofs NEWdIRECTORYnAME /path/to/your/NEWdIRECTORYnAME (the first name has to be the same as you entered in your Qemu settings a minute ago). Now it should be working on both sides.

(If you want to screenshot first, and want to rotate the screen: xrandr -o left (and use xrandr -o normal to return to regular view).)

Open Terminal in the folder with all the images and

convert *.png -shave 90x280 shaved*.png