The path is:
Settings > Skin Settings > Cockpit > Menu Buttons > Cockpit Buttons, (or Quick Menu Buttons) > Show button Picture in Cockpit, (or Show button Picture in Quick Menu).

The bad thing is that it presents images in order of proximity, the scrolling is not very responsive and the image search is complicated.

The option New Route > Picture is grayed out.

I much prefer the system adopted for Luna, it lets me choose between the phone's image management apps, (Gallery or Photos) where the images are not sorted by proximity and are found more easily and quickly.

The option New Route > Picture is selectable and with the same options as the Button described above.