Image

What is a .otg file?

A .otg file is an OpenDocument Graphics (version 1.0). This is an image format — a picture, drawing or graphic. Confusingly, this extension has been used by 3 different formats over the years — they're all listed below.

This extension has been used by more than one format

3 different formats have claimed .otg over the years, so two files with the same extension aren't necessarily the same kind of thing.

How to open a .otg file

GIMP (free) and IrfanView open a very wide range of image formats, including obsolete ones.
XnView MP is the best bet for unusual or legacy image types.
Your operating system's built-in viewer may work for mainstream formats.

The registry records this extension against OpenDocument Graphics, OpenDocument Graphics, OpenDocument Graphics, so software from that family is the most likely match.

How to convert a .otg file

Open it in GIMP or XnView and export as .png (lossless) or .jpg (smaller).

MIME type

When a .otg file travels over the web, servers label it with this MIME type:

application/vnd.oasis.opendocument.graphics

What's a MIME type?

The technical record

For archivists, developers and the merely curious: these are the PRONOM registry entries for .otg.