Acrgis pro version 2.1.1 cannot detect a raster image of format .ecw
ECW format is not enabled until a 3rd party library is updated for Esri. It is expected to be supported by early Q2, 2018.
Source: Release notes for ArcGIS Pro 2.1—ArcGIS Pro | ArcGIS Desktop
The following bug was fixed at ArcGIS Pro 2.1.2.
Release notes for ArcGIS Pro 2.1—ArcGIS Pro | ArcGIS Desktop
Also in ArcMap 10.6, this issue can be resolved by applying the following patch.
ArcGIS (Desktop, Engine) 10.6 ECW Patch
Retrieving data ...