To composite one or more images together using an imaging program (like Photoshop) so perfectly, it is difficult to tell the image is fake.
The photo of Mt. Fuji composited with the ash plume from Mt. St. Helen errupting was so seamless I almost didn't realize it was a fake.
Seamless (noun) - Used to describe a situation where everyone is told it will work perfectly, when in fact it's an unmitigated clusterfuck.
Support Agent: The transfer of your service will be seamless.
Raging Old Person: THEN WHY THE F**K ISNT IT WORKING
Support Agent: Uhh, let me talk to an engineer...