Bug 190981 The image id of image in different pages are the same
The id of image generated by the same report item (such as chart) are the same, thought the image contents are in different pages.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/Image.java
public void writeImage( File dest ) throws IOException
	{
		if ( source == IImage.INVALID_IMAGE )
		{
			logger.log( Level.SEVERE, "image source {0} is not valid!", id ); 
			return;
		}
		InputStream input = getImageStream();
		if ( null == input )
		{
			logger.log( Level.SEVERE, "image source {0} is not found!", id ); 
			return;
		}
		
		
		String parent = new File( dest.getAbsolutePath( ) ).getParent( );
		File parentDir = new File( parent );
		if ( !parentDir.exists( ) )
			parentDir.mkdirs( );
		OutputStream output = null;
		try
		{
			output = new BufferedOutputStream( new FileOutputStream( dest ) );
			copyStream( input, output );
		}
		catch ( IOException ex )
		{
			logger.log( Level.SEVERE, ex.getMessage( ), ex );
		}
		finally