Geeqie is pretty much my favorite image viewer. Even though it's maybe a bit more "heavy-weight" than some others, it's very fast, very flexible (it allows a lot of configuration to make its behavior in various non-default circumstances exactly how one likes), and has great image quality even when scaling (and allows you to choose the scaling filter for those times when you intentionally want only "nearest" filtering, for instance). I like the fact that it is oriented more around viewing directories of images, and does a great job of it, but also allows you to hide all the directory-related UI grot and just focus on the current image I love the fact that it handles partially-written image files without complaint (some image viewers just fall over and die), and will automatically re-read an image that has changed, without messing up the current view even if one has zoomed and panned in the partial image! In general, Geeqie just seems to do "the right thing" more often than other image viewers. [E.g., if you zoom and pan to see a small detail of an image, then hitting the SPC or BS keys to move to the next or previous image in the directory will keep your position and zoom level if possible, which makes it wonderful for doing inter-image comparison of fine details...]
Another half baked, abandoned Linux application. Stupid thing is starting in root folder every time and no way to set a startup folder.
Add a 'filter filenames' (just helpful, there is in all applications), and do what you want with the 'Marks options' (clumsy).