public void setModificationTime(Date modificationTime) {
        this.modificationTime = modificationTime;
        modificationTimeSet = true;
    }
Sets the modification time, as a <code>Date</code>, to be
stored with this image.  The internal storage format will use
UTC regardless of how the <code>modificationTime</code>
parameter was created.

<p> The 'tIME' chunk will encode this information.
plugins/svg-plugin/batik-codec-fix/src/main/java/org/apache/batik/ext/awt/image/codec/png/PNGEncodeParam.java