Change an image during animation using storyboard

I was looking for a way to change an Image during a storyboard, or more specifically, change the Source property of the image to point to a new image resource. There seems to be a StringAnimationUsingKeyFrames and a DiscreteStringKeyFrame but this does not work (as far as I can tell) since the Source property of the Image is of type ImageSource

My current storyboard looks like this

<Storyboard x:Key="TransitionImage">
    <DoubleAnimationUsingKeyFrames
        BeginTime="00:00:00" 
        Storyboard.TargetName="image" 
        Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[0].(ScaleTransform.ScaleX)">
        <SplineDoubleKeyFrame KeyTime="00:00:00.7000000" Value="0.2"/>
        <SplineDoubleKeyFrame KeyTime="00:00:01.5000000" Value="1"/>
    </DoubleAnimationUsingKeyFrames>
    <StringAnimationUsingKeyFrames
        BeginTime="00:00:00"
        Storyboard.TargetName="image"
        Storyboard.TargetProperty="(Image.Source)">
        <!-- This does not work -->
        <DiscreteStringKeyFrame KeyTime="00:00:00.7000000" Value="check_24.png"/>
    </StringAnimationUsingKeyFrames>
    <DoubleAnimationUsingKeyFrames 
        BeginTime="00:00:00" 
        Storyboard.TargetName="image"
        Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[0].(ScaleTransform.ScaleY)">
        <SplineDoubleKeyFrame KeyTime="00:00:00.7000000" Value="0.2"/>
        <SplineDoubleKeyFrame KeyTime="00:00:01.5000000" Value="1"/>
    </DoubleAnimationUsingKeyFrames>
</Storyboard>

and the image

<Image x:Name="image" 
       Source="delete_24.png"
       Width="32" Height="32"
       Margin="8"
       RenderTransformOrigin="0.5,0.5">
    <Image.RenderTransform>
        <TransformGroup>
            <ScaleTran