You can use PNG or SVG images. PNG is a low-resolution image format. You can use a PNG for icon images and screenshots without call-out text. SVG is a high-resolution image format. In addition to being clearer, call-out text that you add to an SVG can be localized. Therefore, SVG is a good choice for topologies and screenshots that require call-out text. Using an SVG eliminates the need to use numbered call-outs with a table underneath the image. For more information about SVG images, see DITA and Tridion Docs Work Instructions and Guidelines.