IMV

IMV is a feather-light image viewer that focuses on speed and system resources. It contains several navigation controls accessible via keyboard shortcuts, offering support for JPG, PNG, BMP, ICO and TIFF file types.

Lightweight and portable graphic viewer

Setup isn't necessary. The downloaded package includes an executable file for IMV, along with another one that represents a stripped down version of it, which is a bit lighter and can be used if you have GDI+. It doesn't configure system registry settings or create new files on the disk. It's only necessary to delete the files to perform an uninstall.
A file browser pops up on the screen when launching the application, asking you to find and select an image file. It's opened in a minimalistic window that doesn't contain any buttons or menus, and which exits on mouse right click.

Fullscreen, image borders, slideshow, and sharp effect

The list of available commands accessible through hotkeys can be displayed by hitting the F1 key, such as entering fullscreen mode, zooming in and out, opening the previous or next image in the current directory, opening a new image via the file browser, or toggling the image border.
Additionally, you can put together a slideshow from all pictures from the current directory, sharpen photos when upscaling, copy file names to the Clipboard, or launch a new instance of the application. Some mouse controls are available too, like dragging the window's margins for resize.

Configure several program settings

There's also a preferences panel that gives you the possibility to customize the background color for transparent images (e.g. PNGs with transparency), hide the border and file name label, or disable high-quality resizing. The default settings for label font height, screen time for slides (seconds), and size of the image cache (megabytes) can be altered too. Command lines are supported.
In conclusion, IMV is not so modest as it may have users believe. It felt light and loaded pictures fast without affecting the computer's performance or other running applications in our tests.