Word (and indeed PowerPoint, Excel, Publisher) doesn't have an image format
per se it uses the proprietrary formats .doc and more recently .docx (although it can save to other formats such as .rtf and .html and so forth).
Perhaps what you have is an image
embedded within a word document. This image may be one of many formats such as .wmf (Windows Met-file), .jpg (GPEG), .bmp (bit-map), .png (Portable Network Graphics) and so forth.
To get the best resolution copy of the image (assuming you don't have access to the original), you probably want to open the word document up, scroll to the image and left-click on it once. This selects the image, you can now right-click and select copy, which will copy the image to your clipboard.
Now open up Paint/
IrfanView/
GIMP/other image program and paste this into a new image, then save it as one of the above described image formats or one of your choice (optimal choice will depend on the intended use of the image).
slack
See
here for a fairly complete list of file formats.