Karis Hedges was returning from Skomer Island, Pembrokeshire, when she saw the seal "chilling out".
The 26-year-old started snapping away and captured some "lucky shots" of the mammal in the inflatable boat.
Ms Hedges, from Llandeilo in Carmarthenshire, said she was really surprised to see the seal.
The large animal, blatantly unbothered by its audience appeared completely relaxed.
Photos taken by Ms Hedges, who is a full-time photographer, show the brazen seal peering up towards its onlookers on 19 May.
Ms Hedges added that the boat was coming into shore and was moving quite quickly, so she only had a few seconds to capture the image.
"I thought it was really cute that he was totally unfazed by anyone and just chilling out without a care in the world.
"His expression is like 'and? Do you have a problem?' Like it was the most normal thing," she said.
Ms Hedges said she believed the seal had climbed into a boat's rescue dingy, adding the crew would probably have to kick out the surprise guest at the end of the day.
Karis Hedges who captured the image says the seal was acting like it was "the most normal thing" to do.
www.bbc.com