I've used GDAL tools for several other operations on GeoTIFFs.
There is lots of information on how to splice geotiffs into pgw world files and images, but I havent found ANY documentation on how to properly CREATE a geotif from an image and and a worldfile (plus CRS format info).
This can be done by loading a layer in QGIS and exporting it as GeoTIFF, but need to use the GDAL commandline directly for batch conversions.
I've found one somewhat related question, which use world files as input. GDAL rotate DEM But despite GDAL created the file without showing errors, the file was unreadeable.
gdal_translate -of GTiff -co profile=baseline -co tfw=yes geotiff.tif baseline.tif
This also lead to an unreadeable file.
gdal_translate -of GTiff -co COMPRESS=JPEG -co tfw=yes -a_srs EPSG:3857 geotiff.tif baseline.tif