Ubuntu 18.04 / iOS 11.4

This version of Ubuntu has the latest libimobiledevice (at the time of release) so it supports iOS 11.4. There is a propblem with the Gnome integration, though. It shows the Documents folder (app folders). In addition to the tip below by @diego, here's a simple way to get to the pictures folder (this works if the iOS Documents show up for you but not the pictures):

• Open the iDevices Documents folder in Nautilus.
• Press CTRL+L to get the real address which will look like afc://YOURSERIAL:3/
• Remove trailing colon and number and press ENTER (i.e. it should just read afc://YOURSERIAL)

You should now see your iDevices system folders, including DCIM.

Ubuntu 17.04 / iOS 10.3.3

As a workaround, you can mount your iOS device with ifuse.

sudo apt install ifuse

Now connect your device and make sure it is paired with your computer.

idevicepair validate

If you get a SUCCESS message, you are good, if not run idevicepair pair. Now you can use ifuse to mount your iOS images folder:

mkdir ~/pics && ifuse ~/pics

The images are now available in your $HOME folder under pics. Ready to be synced with Shotwell. To unmount the folder, use fusermount:

fusermount -u ~/pics && rmdir ~/pics

Note: in this example I create a pics folder and remove it afterwards. If you already have a folder named like this, choose a different name.

Upgrading usbmuxd solves the issue. I downloaded a newer package from https://packages.ubuntu.com/cosmic/usbmuxd (1.1.1~git20180428.b95a0a0-1) and installed it. Surprisingly, it was compatible with Ubuntu 18.04.