There are two ways that images (or files related to images) are saved in SMS.
When a project file is saved any images that are part of the project are saved. Also, the registration information is saved in the project file to provide the coordinate system information for the image.
When the File | Save As command is selected, one of the options listed in the set of filters is a Bitmap file (*.bmp). This option is used to save a bitmap image of whatever is currently being displayed in the Graphics Window (grids, solids, boreholes, cross sections, images, etc.). When saving a bitmap, you can specify a higher resolution at which to create the bitmap. This may be useful if you need to enlarge the image. The resolution can be changed using the Edit | Preferences command and clicking on the General tab.
A World File can be exported for the selected image by right-clicking on the Project Explorer and selecting the Export World File command. A world file is a special file that contains registration data that can be loaded into GMS and used to register images.