You can export any images out of .otg files using one of the open source office suites based on the Open Document schema, such as OpenOffice.org or LibreOffice. The Draw program which is part of these suits uses .otg files for templates. If any images are present in these templates you should be able to save them in one of the typical image formats like JPEG.
Convert OpenOffice.org graphics document template to JPEG bitmap image format.
We have found 2 software records in our database eligible for .otg to .jpg file format conversion.
Multiplatform software - convert otg to jpg on any platform
Graphic editor for diagrams and simple graphics from OpenOffice.org suite
Convert from otg file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned otg to jpg. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Graphic and diagram software from LibreOffice suite