The jpeg analyzer (libstreamanalyzer/plugins/endplugins/jpegendanalyzer.cpp) stores all properties as strings. This is neither correct nor very useful. Many of the properties are actually numbers and there is one very important one: the creation date. If it is stored as a string its value becomes useless. The correct types of the properties can be seen in http://oscaf.svn.sourceforge.net/viewvc/oscaf/trunk/ontologies/nexif/nexif.trig?view=markup.