Avalonia/samples/ControlCatalog/Pages/ImagePage.xaml

<UserControl xmlns="https://github.com/avaloniaui">
  <StackPanel Orientation="Vertical" Spacing="4">
    <TextBlock Classes="h1">Image</TextBlock>
    <TextBlock Classes="h2">Displays an image</TextBlock>

    <StackPanel Orientation="Horizontal"
                Margin="0,16,0,0"
                HorizontalAlignment="Center"
                Spacing="16">
      <StackPanel Orientation="Vertical">
        <TextBlock>No Stretch</TextBlock>
        <Image Source="resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg"
               Width="100" Height="200"
               Stretch="None"/>
      </StackPanel>

      <StackPanel Orientation="Vertical">
        <TextBlock>Fill</TextBlock>
        <Image Source="resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg"
               Width="100" Height="200"
               Stretch="Fill"/>
      </StackPanel>

      <StackPanel Orientation="Vertical">
        <TextBlock>Uniform</TextBlock>
        <Image Source="resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg"
                Width="100" Height="200"
                Stretch="Uniform"/>
      </StackPanel>

      <StackPanel Orientation="Vertical">
        <TextBlock>UniformToFill</TextBlock>
        <Image Source="resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg"
               Width="100" Height="200"
               Stretch="UniformToFill"/>
      </StackPanel>
    </StackPanel>
    <StackPanel Orientation="Vertical">
      <TextBlock>Window Icon as an Image</TextBlock>
      <Image Name="Icon" Width="100" Height="200" Stretch="None" />
    </StackPanel>
  </StackPanel>
</UserControl>