Georeference an image in SNAP

How can I georeference an image in SNAP?

More information is needed to understand your problem. If your image is mapped and sized to match an existing product in SNAP you may be able to use the Raster Merge operator to add your image as a new band in an expanded product.

If that fails you may be able to add navigation metadata to the image (examples of this using snappy can be found in this forum). If your image does not have any existing matching product you may want to use GIS tools (QGIS, etc) or GDAL. For GDAL you may be able to specify the navigation metadata in a “virtual raster table” (.vrt file) to generate a georeferenced file. I have used this with some products that are provided in PNG format with known (global lon-lat) mapping.

You can also use Ground Control Points.
I explained it briefly in this post: