I have an email (Gmail) with multiple image attachments that I would like to save to one of my folders. I know you can do "Download all attachments" using Gmail, but I would like to give my images a specific name. In particular, I would like the images to be numbered starting from 10 (so first image attachment should be called 10, second should be called 11, etc...). Is there a quick way to do this, perhaps with the command line (or otherwise)?
I can't provide a procedure to download your files with a specific name each, but you can -as you mentioned- use the "Download all attachments" both in GMail or another mail client, such as Thunderbird, Evolution, etc.
Once you finish downloading your attachments, you can use Dolphin or Thunar file managers, and if you need more control on your files and the new names you can use pyrenamer.
Dolphin
After extracting/moving your files, you can select all your files and press F2 in order to show the rename dialog, where you can setup a new name with a numbers sequence and tell which number you may wish to start the sequence.
Thunar
You can do exactly the same as in the process described above for Dolphin file manager, the dialog is a bit different and allow you to choose what information you want to use for renaming the files, as shown in this screenshot.
Pyrenamer
Pyrenamer is such a Swiss Army Knife, with all the tools you may need to rename any amount of files with ease.
No need to say more. You need to try it.
I hope this may help you as it does for me.