I believe the term you're looking for is the happily intuitively named ghost, which is briefly defined as "a spurious image resulting from an echo".
A more in-depth definition can be found on the dedicated Wikipedia page for video ghosts:
In television, a ghost is a replica of the transmitted image, offset in position, that is super-imposed on top of the main image. It is often caused when a TV signal travels by two different paths to a receiving antenna, with a slight difference in timing.
The more general term for unintentional issues during rendering is artifact. From Wikipedia's glossary of video terminology:
A defect or distortion of the video image, introduced along the sequence from origination and image capture to final display. Artifacts may arise from the overload of channel capacity by excess signal bandwidth. Artifacts may also result from: sampling effects in temporal, spatial, or frequency domains; processing by the transfer functions; compromises and inadequacies in the system employed; cascading of minor defects; basically any other departure of the total system from “complete transparency” resulting in visual errors.
A related term is noise, mostly used for widespread and random effects impacting the entire image (like snow on old TV sets or static on the radio).
If there is a more specific term, I didn't find it in a quick scan of that entire glossary.