The query returns:

select pv.dataType, pv.pointValue, pva.textPointValueShort, pva.textPointValueLong, pv.ts, pva.sourceType, pva.sourceId from pointValues pv left join pointValueAnnotations pva on pv.id = pva.pointValueId where pv.id=9467

DATATYPE: 5
POINTVALUE: 1
TEXTPOINTVALUESHORT: 9467
TEXTPOINTVALUELONG: null
TS: 1342218110819
SOURCETYPE: null
SOURCEID: null

The new ImageValue constructor uses the textpointvalueshort of 9467 to determine the filename, and the pointvalue 1 to determine the file extension.

public class ImageValue extends MangoValue implements Comparable<ImageValue> {
    private static final String FILENAME_PREFIX = "img";

    public static final int TYPE_JPG = 1;
    private static final String[] TYPES = { "", "jpg" };

    private long id = Common.NEW_ID;
    private int type;
    private byte[] data;

    public ImageValue(long id, int type) {
        this.id = id;
        this.type = type;
    }

    public ImageValue(byte[] data, int type) {
        this.data = data;
        this.type = type;
    }
...

Therefore in PointValueDao.java

    MangoValue createMangoValue(ResultSet rs, int firstParameter) throws SQLException {
        int dataType = rs.getInt(firstParameter);
        MangoValue value;
        switch (dataType) {
        case (DataTypes.NUMERIC):
            value = new NumericValue(rs.getDouble(firstParameter + 1));
            break;
        case (DataTypes.BINARY):
            value = new BinaryValue(rs.getDouble(firstParameter + 1) == 1);
            break;
        case (DataTypes.MULTISTATE):
            value = new MultistateValue(rs.getInt(firstParameter + 1));
            break;
        case (DataTypes.ALPHANUMERIC):
            String s = rs.getString(firstParameter + 2);
            if (s == null)
                s = rs.getString(firstParameter + 3);
            value = new AlphanumericValue(s);
            break;
        case (DataTypes.IMAGE):
            value = new ImageValue(Integer.parseInt(rs.getString(firstParameter + 2)), rs.getInt(firstParameter + 3));
            break;
        default:
            value = null;
        }
        return value;
    }

should be

...
        case (DataTypes.IMAGE):
            value = new ImageValue(Integer.parseInt(rs.getString(firstParameter + 2)), rs.getInt(firstParameter + 1));

changing the column used to load the image type from the fourth column to the 2nd gives the image the correct type (1 for jpg) and subsequently the correct file extension is used when loading images for the flipbook, otherwise "img9467." is loaded by the imageValueServlet, which doesn't exist, and 0 byte images are returned result.