src/org/tiefaces/components/websheet/dataobjects/CellMap.java
private String loadChart(final int rowIndex, final int colIndex) {

		FacesCell facesCell = parent.getCellHelper()
				.getFacesCellWithRowColFromCurrentPage(rowIndex, colIndex);
		if (facesCell != null && facesCell.isContainChart()) {
			FacesContext context = FacesContext.getCurrentInstance();
			String chartId = facesCell.getChartId();
			String chartViewId = Integer.toHexString(
					System.identityHashCode(parent.getWb())) + chartId;
			if (context != null) {
				Map<String, Object> sessionMap = context
						.getExternalContext().getSessionMap();
				if (sessionMap.get(chartViewId) == null) {
					sessionMap.put(chartViewId, parent.getCharsData()
							.getChartsMap().get(chartId));
				}
			}
			return chartViewId;
		} else {
			return null;
		}
	}
private String loadChart(final int rowIndex, final int colIndex) {

		FacesCell facesCell = parent.getCellHelper()
				.getFacesCellWithRowColFromCurrentPage(rowIndex, colIndex);
		if (facesCell != null && facesCell.isContainChart()) {
			FacesContext context = FacesContext.getCurrentInstance();
			String chartId = facesCell.getChartId();
			String chartViewId = Integer.toHexString(
					System.identityHashCode(parent.getWb())) + chartId;
			if (context != null) {
				Map<String, Object> sessionMap = context
						.getExternalContext().getSessionMap();
				if (sessionMap.get(chartViewId) == null) {
					sessionMap.put(chartViewId, parent.getCharsData()
							.getChartsMap().get(chartId));
				}
			}
			return chartViewId;
		} else {
			return null;
		}
	}
Put chart image to session map and return the key to web.

@param rowIndex
the row index of the cell which contains picture.
@param colIndex
the column index of the cell which contains picture.
@return the key of the picture image in the session map.