I used the graphic software program GIMP to manipulate a geoTIFF image (GIMP cannot handle geoTIFFs, so after manipulating the image in GIMP the geospatial information is lost).
When I now try to import the manipulated TIFF into ArcGIS 10.3.1, for some strange reason Arc displays the original TIFF image without any of the alterations I made in GIMP (outside ArcGIS, I see the manipulated version though)