The XML-based annotation format was introduced by the PASCAL Visual Object Classes.
Here is an example:
<annotation>
<folder></folder>
<filename>image_0001.jpg</filename>
<path>image_0001.jpg</path>
<source>
<database>Unknown</database>
</source>
<size>
<width>689</width>
<height>500</height>
<depth>3</depth>
</size>
<segmented>0</segmented>
<object>
<name>Daffodil</name>
<pose>0</pose>
<truncated>0</truncated>
<difficult>0</difficult>
<occluded>0</occluded>
<bndbox>
<xmin>86</xmin>
<xmax>583</xmax>
<ymin>80</ymin>
<ymax>388</ymax>
</bndbox>
</object>
</annotation>