Power Outage - S3-E7
Revealing mistake: Alyssa's tattoo is visible when Phoebe leaves Cole's apartment after she fought with her sisters.
Revealing mistake: When the prince is supposed to be frozen on Paige's living room couch, when they do a close-up you can see the actor blink.
Revealing mistake: As Phoebe and Rick are in the car about to do the robbery, she pulls out in front of the armoured van and as she drives out onto the road you see Phoebe's stunt doubles face.
Revealing mistake: When Prue talks about her relationship with Justin near the beginning of the episode, she says that she finds him to be very predictable, lacking in mystery or "savoir-faire." That doesn't make sense, though, as "savoir-faire" means "know-how." She probably meant "je ne sais quoi," that is, "I know not what."
Revealing mistake: When Piper blows up the painting you can see the hole used to put the charge into to blow it up. (00:57:40)
Revealing mistake: When Leo dropped the Grimlock potion, it was obviously fake when it hit the ground.
Coyote Piper - S3-E9
Revealing mistake: After Phoebe has her premonition in the mausoleum, she wipes away the dust from the crypt to reveal Cole's father's name. Just BEFORE they show her wiping the dust away, you can see the letters in the shot of her leaning against the crypt.
House Call - S5-E13
Revealing mistake: When Piper made the house vanish, and she, Paige and Leo ran up to where it was, the background was obviously fake. (00:35:35)
The Truth Is Out There... and It Hurts - S1-E8
Revealing mistake: When Phoebe asks Piper what she thinks of her boss, you can see that Holly's tattoo has been covered up, because that part of her wrist is darker than her skin. (00:17:15)
Revealing mistake: When Piper is being spun in the web, she spins around and gets stuck to the wall. If you look closely Chris's eyes look above the CGI figure and do not follow it correctly.
Charmed and Dangerous - S4-E13
Revealing mistake: At the end of the episode after Phoebe and the Seer put the hollow away in its place, she leaves, but when it next cuts to a closeup of Cole, in the corner of the screen you can see her hair. (00:41:50)
Revealing mistake: When Phoebe punches Dr. Williamson, it's easy to tell that she doesn't really punch him.
Revealing mistake: The sheet-covered body of Charlene that is being moved by the police has obviously got a head, despite the fact that she was meant to have been decapitated.
Revealing mistake: When Maggie Murphy climbs onto the ledge of the roof to jump off you can see the surface of the ledge dipping as if it was foam.
Be Careful What You Witch For - S2-E22
Revealing mistake: During the search for the Dragon and teenage Prue, Phoebe's wearing a red top and red jacket, but when Phoebe lands on the ground we can see the bulky beige material of the stunt vest at her back, under the red top and jacket. (00:34:05)
Revealing mistake: The sound of Phoebe writing with a permanent marker was added in, as you can see that the marker never touches the paper. Then after a few seconds Phoebe stops writing to listen to Prue and her marker isn't moving but the sound of writing can be heard. (00:05:30)
Pre-Witched - S3-E17
Revealing mistake: At the beginning of the episode Piper and Leo are in the shower together - at the bottom of the screen you can see Piper has on a flesh colored towel.
Revealing mistake: In Chris's flashbacks, it's supposed to be the day he left to come to the future. But his hair is longer than it was in the season 5 finale when he came to the future.
Love Hurts - S1-E21
Revealing mistake: After Piper saves Leo, they meet with Phoebe and Daisy downstairs near the living room. Before the darklighter appears, smoke from a fog machine can be seen at the left of the shot to magically transition to the computerized effects. (00:33:45)
Revealing mistake: When Phoebe and Paige use Cole as bait to lure Piper to the manor, Phoebe levitates and kicks two furies at once. When they show the front shot of her kicking these two furies, we can see Alyssa Milano's stunt double. (00:34:25)
Suggested correction: Maybe Holly covered it up with makeup because she isn't supposed to have tattoos for her job? A lot of jobs still don't allow piercings and tattoos today but all those years ago it was even harsher.
There are multiple instances of covered tattoos during the early seasons. I noticed it the most on Alyssa's back tattoo.