Warning: the following gallery include screenshots from unstable and unreleased versions.
GNOME and Budgie
The primary menu opened (version 0.4.8)
The "selection" tool and its menu (version 0.4.8)
The "arc" tool and its options (version 0.4.8)
Change the saturation (version 0.4.8)
The "new images" menu opened (version 0.4.7)
Select a color (version 0.4.7)
Add text to a picture (version 0.4.1)
Zooming on the image (version 0.5.3-unstable)
Cinnamon and MATE
The Cinnamon user interface (version 0.4.8)
Scaling the picture with the colorful icons of the MATE user interface (version 0.4.7)
It's also possible to use only the toolbar, or only the menubar. The user interface you will get by default depends on your desktop environment, but you can change that in the app preferences.
Toolbar only, with the preferences window (version 0.5.3)
The elementaryOS design guidelines (version 0.2)
Using the primary menu to show the tools names (version 0.4.8)
With the default "GNOME" layout, the window can fit in the narrow screen of a smartphone such as Purism's Librem 5 or the PinePhone.
Here is a youtube screencast on the devkit (version 0.2).
When features can't fit in the headerbar, they are available from the primary menu (version 0.4.8)
Pencil options menu on a window resized to fit a Librem 5 screen. Notice that my fonts are smaller than the default GNOME settings (version 0.4.7)