The Jet Propulsion Laboratory makes images available for download through their WMS service. Landsat7 visual images, SRTM magnetic resonance, Landsat7 infrared...
I made an app that can download LOD8 ( cell sized ) images to the folder of your choice. They are WGS84 geographic, and you can make a text file that allows them to be imported as a map to SBuilder. The bounds in that text file can also be used for Ground2K(4).
You can manually enter decimal degrees or rip them from Google Earth or from any FS product that has FSUIPC. The LOD8 bounds containing that coordinate will be downloaded. 1024x1024, 2048x2048, and 4096x4096 are provided sizes. The smaller files will be a much quicker download. You may need to try a few times to get the data, as the JPL servers are often overworked and underpaid.
Get it here:
Or visit my SkyDrive for the tool:
JPLDownLoad at SkyDrive
The Landsat pseudo is pretty good for tracing. The SRTM magnetic reflectance is good for detecting shorelines beneath cloud-cover. The infrared can be used ( in some cases) to detect water and coastlines... you can sometimes make a mask by loading the image into a paint program, and using the magic wand to select the darkest colors, thereby grabbing the water.
Ground2K and SBuilder will need the images converted to bitmaps. SBuilderX is OK with PNG images.
None of these images are suitable for photoreal.