Can I set the base path outside of my application directory when binding an image source path to a relative path in WPF?-Collection of common programming errors

Declare a static field say BasePath in code behind

class Utility
{
    public static BasePath;
}

assign it the path that you want to use as base path

declare a converter like this:

public class RelativePathToAbsolutePathConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        //conbine the value with base path and return
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // return whatever you want
    }
}

Update your binding to use a converter