using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace CustomControls
{
    [TemplatePart(Name="CLIPRECTANGLE", Type=typeof(RectangleGeometry))]
    public class ImageProgressBar : ProgressBar
    {
        public ImageProgressBar()
        {
            this.DefaultStyleKey = typeof(ImageProgressBar);
        }

        public ImageSource Source
        {
            get { return (ImageSource)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }

        public static readonly DependencyProperty SourceProperty =
            DependencyProperty.Register("Source", typeof(ImageSource), typeof(ImageProgressBar), new PropertyMetadata(null));

        public Brush Fill
        {
            get { return (Brush)GetValue(FillProperty); }
            set { SetValue(FillProperty, value); }
        }

        public static readonly DependencyProperty FillProperty =
            DependencyProperty.Register("Fill", typeof(Brush), typeof(ImageProgressBar), new PropertyMetadata(null));

        private RectangleGeometry _clip;

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            _clip = this.GetTemplateChild("CLIPRECTANGLE") as RectangleGeometry;
            this.ValueChanged += ImageProgressBar_ValueChanged;
            this.SizeChanged += ImageProgressBar_SizeChanged;
        }

        void ImageProgressBar_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            UpdateClip();
        }

        void ImageProgressBar_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            UpdateClip();
        }

        private void UpdateClip()
        {
            if (_clip != null)
            {
                _clip.Rect = new Rect(0, 0, this.ActualWidth, this.ActualHeight * ((this.Value - this.Minimum) / (this.Maximum - this.Minimum)));
            }
        }
    }
}

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:CustomControls">
    <Style TargetType="local:ImageProgressBar">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="local:ImageProgressBar">
                    <Border BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Margin="{TemplateBinding Margin}"
                            Background="{TemplateBinding Background}"
                            Width="{TemplateBinding Width}"
                            Height="{TemplateBinding Height}">
                        <Grid>
                            <Image Source="{TemplateBinding Source}"
                                    Stretch="Fill" />
                            <Rectangle Fill="{TemplateBinding Fill}">
                                <Rectangle.OpacityMask>
                                    <ImageBrush ImageSource="{Binding Path=Source, RelativeSource={RelativeSource TemplatedParent}}"
                                                Stretch="Fill" />
                                </Rectangle.OpacityMask>
                                <Rectangle.Clip>
                                    <RectangleGeometry x:Name="CLIPRECTANGLE" />
                                </Rectangle.Clip>
                            </Rectangle>
                        </Grid>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

</ResourceDictionary>

<my:ImageProgressBar Width="100"
                     Height="100"
                     Fill="Red"
                     Source="ProgressBar.png"
                     Minimum="100"
                     Maximum="200"
                     Value="{Binding ElementName=slider1, Path=Value, Mode=TwoWay}" />
<Slider Margin="0"
        Name="slider1"
        VerticalAlignment="Top"
        Minimum="100"
        Maximum="200"
        Value="125" />