general: added images

wiki/images.md

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+# Images
+
+An image is a visual representation of something.
+In the computer context it is a file with an extension like `png`, `jpg`, `gif` among others.
+
+## Clients
+
+- [sxiv](https://github.com/xyb3rt/sxiv) is an image viewer for [Linux'](/wiki/linux.md)
+  [X window system](/wiki/linux/x_window_system.md).
+
+## Editing
+
+Editing images can be done by various image manipulation software.
+A popular cross-platform program for this is [GIMP](https://www.gimp.org/).
+
+Another part of image manipulation is the upscaling of low resolution images.
+This can be done by the cross-platform program [upscayl](https://github.com/upscayl/upscayl).