This will display random image from specified media library (Backgrounds):
<img src="~/MEDIOClinic/media/backgrounds/{% fileIndex = Math.GetRandomInt(0, SiteObjects.MediaLibraries["Backgrounds"].Files.Count-1);
SiteObjects.MediaLibraries["Backgrounds"].Files[fileIndex].FilePath %}" />

This will display random image from specified media library (Backgrounds) with limited width:
<img src="~/getmedia/{% fileIndex = Math.GetRandomInt(0, SiteObjects.MediaLibraries["Backgrounds"].Files.Count-1);
SiteObjects.MediaLibraries["Backgrounds"].Files[fileIndex].FileGUID %}/img?width=320" />

This will display HTML5 Picture element with random image from specified media library (Backgrounds):
{% fileIndex = Math.GetRandomInt(0, SiteObjects.MediaLibraries["Backgrounds"].Files.Count-1);
fileGUID = SiteObjects.MediaLibraries["Backgrounds"].Files[fileIndex].FileGUID;
fileURL = "~/getmedia/" + fileGUID + "/img"; "" %}
      <picture>
        <source media="(min-width: 650px)" srcset="{% fileURL %}?width=1200" />
        <source media="(min-width: 465px)" srcset="{% fileURL %}?width=650" />
        <!-- img tag for browsers that do not support picture element -->
        <img src="{% fileURL %}?width=200" />
      </picture>

This will display image based on GUID (for images stored within Pages) and is code from transformation:
<img src="~/CMSPages/GetFile.aspx?guid={% Photo %}&width=320" />