From the movie Dagon
From the classic Bride of Frankenstein
From the movie Analyze This; Robert de Niro and Billy Crystal talk in front of an aquarium in which two young ladies dressed as mermaids cavort
From the movie Night Tide
Screen captures from a Big Lots commercial, the movie Beach Blanket Bingo, the Night Gallery episode "Lindemann's Catch", a commercial for some fruit drink whose name I missed, the music video Oo-ee-diddly-bop, the TV movie Princess, Viva Maria starring Brigitte Bardot, and the Superman: The Animated Series episode "Live Wire".
Cartoon Screencaps from the TV shows Go, Diego, Go!, Dora the Explorer, Little Bear, and Backyardigans.
More screencaps from the movies The Thirteenth Year, Enchanted, Local Hero, and Roxy Hunter and the Myth of the Mermaid, the TV shows Charmed, Mapp & Lucia, and Miami Ink, a commercial for metro PCS, and the History Channel's documentary World War I. (The caps are of a propaganda movie at the time where King Neptune is informed by mermaids of Britain's peril and goes to the surface to exhort the British to buy war bonds.)