WPF image button

In WPF an Image button is simply a Button with its Content set to an image. So, if you want to change the image, you simply need to assign another image to the Content property of the Button.

You cann't change Image, since in WPF Button is just a button as @Daniel Hilgarth wrote. However you can make new style for button like - and apply it to your buttons. This might work like your requirements.

        <Style x:Key="BtnStyle" TargetType="{x:Type Button}">
            <Setter Property="OverridesDefaultStyle" Value="true" />                
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Button}">
                        <Grid>
                            <!--Image-->
                            <Image x:Name="BtnImage" Stretch="Fill" />
                            <ContentPresenter Margin="2" HorizontalAlignment="Center" RecognizesAccessKey="True" VerticalAlignment="Center" />
                        </Grid>
                        <ControlTemplate.Triggers>
                            <!--Trigger for IsEnabled-->
                            <Trigger Property="IsEnabled" Value="false">
                                <!--Set the source of the image-->
                                <Setter TargetName="BtnImage" Property="Source" Value="pack://application:,,,/YouAppShortName;component/Image.png" />
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>