After installing ArcGIS 10.6, I was disappointed to discover that ECW files were not supported. Refer GeoNet. This is a popular format in Australia and I had many raster images stored in ecw format. Unfortunately, because the files were not recognised, I couldn’t even use ArcGIS to convert the images to another format. I decided to roll back to ArcGIS 10.5.1 and wait for ESRI to resolve the problem.
Good news! A patch is now available for 10.6 that allows this version to support the ECW raster format. The reason it was not included in 10.6 was due to a compiler incompatibility. I haven’t installed and tested the patch yet – I will need to revert to 10.6 first.
You can download the patch from ESRI here.