XnView Full is a powerful tool that enables users to view, process, and convert image files easily. XnView Full has all plug-ins and languages included. XnView Standard has just a few add-ons included.
LibreCAD is an Open Source 2D CAD (computer-aided drafting) application that provides an easy-to-use graphics suite for all major operating systems. LibreCAD portable is also available.
Lunacy is a full-fledged sketch editor. Using Lunacy, you can create new designs. It's a perfect tool for prototyping. You can add simple shape elements to your layout (such as drawing an oval, rectangle, line, or adding a bitmap) and drawing, aligning, and joining objects.
PaintOkay is a streamlined and efficient alternative to the traditional MS Paint XP. It prioritizes pixel-editing functionality, allowing you to focus on precise image manipulation without the distraction of nonessential features.
Imagine is a free image-animation viewer developed as an alternative to many other free popular viewers such as IrfanView, XnView, or FastStone Image Viewer.
Artweaver Free lets you paint creatively with the help of a vast range of painting tools so you can create sketches from photos or experiment with colors.
GIMP Portable is the full-featured image and photo editor bundled with a PortableApps.com launcher as a portable app so that you can edit your photos and images on the go. The latest installer is available for download here.
darktable is an Open Source photography workflow application and raw developer intended to be a virtual light table and darkroom for photographers. Portable version is also available.