Carter did, and Rainy saw it right away. “We’ve got the same jarring transition in the same section of both images,” she said.
“The unusual shading pattern looks similar, but they’re not identical,” Carter said. “The pixel colors are different, too.”
“But it’s something,” Rainy said. She was feeling breathless. “Each image looks identical. Only at magnification can we see the actual location of pixel color variation. Why?”
“It’s probably a watermark,” said a voice from behind them.
Rainy turned, and her eyes went wide with delight. Clarence Stern had just entered the Lair.
“Tomlinson said he’ll need that PowerPoint deck by six,” Stern announced. “Now, move over, Carter. Let me figure this out.”
Chapter 72
“You think it’s an invisible watermark?”
“Seems like it to me,” Stern said to Rainy. “Watermarks are nothing more than embedding information into a digital media. Could be audio. Could be a picture.”
“Could be spinning the Beatles’ ‘I’m So Tired’ backward and hearing Paul is dead,” Carter said.
“Well, that’s a watermark of sorts, I guess,” Stern said. “It’s used a lot in copyright protection. It’s also used in source tracing.”
Rainy nodded. “Of course. The movie industry has been using source trace watermarks for ages. They can identify who downloads their intellectual property and then create a map of the distribution network. We’ve been exploring applications for them as well.”
Carter nodded enthusiastically. “If each of the images Mann gave us has a unique watermark, it would explain why they weren’t generating the same hash value. The watermark is what makes each image unique from the other. But it’s hidden, so we can’t easily see the difference with our eyes.”
“The question now is,” Stern said, “how do we reveal the watermark?”
Stern picked one image to work with. He spent a half an hour bumping up the contrast and adjusting the image levels.
“I’ve got the contrast here set to one hundred percent.”
Rainy looked. “See anything?”
“I’ve got to run the contrast filter a bunch of times over before I can say.”
Stern was back to his Stern ways. Grunting. Sighing. Pouting. He picked up a pencil and prepared to throw it at the monitor.
“That’s my monitor, Clarence,” Carter said. “I trust you. But not that much.”
Stern set down the pencil. He looked over at Rainy. “Do you have an original?” he asked.
“What do you mean?”
“An original source. One that hasn’t been moved from a point A to a point B. One that wouldn’t have a watermark applied.”
Rainy thought a moment. “Lindsey Wells,” she said. “After my seminar she gave me her cell phone. She deleted the sent messages, but not the pictures. She thought they might somehow be helpful.”
“Well, she just might be right,” said Stern. “Let me have it.”
Rainy returned to the workstation with Lindsey’s cell phone. It took only a few minutes for Stern to download the pictures to Carter’s machine.
“What are you going to do?” Rainy asked.
“I’m going to run a difference filter,” Stern said.
“I’m not familiar with that,” Rainy said.
“The difference filter compares the original to a copy. Look, I’ll compare the original to itself.”
Stern did just that, and all Rainy saw afterward was a black square on the screen.
“A black square means the images are identical,” Stern explained. “All pixels turned a pure black color. Now let’s run the difference filter on the original and one of the matching images.”
Rainy examined the completed output. “It still looks like a black square to me,” she said.
“But some of the pixels are not quite pure black,” Stern said. “When I change the color levels to brighten all the very dark colors, I suspect our hidden watermark will become visible.”
Stern adjusted the levels. The dark colors transformed to bright, almost neon shades. Rainy’s hand went to her mouth when she saw what appeared. Most of the image square was still black. But not all of it. At the bottom of the square, Rainy saw a series of numbers. Stern’s level adjustment had turned the color of those numbers a bright yellow.
“I bet those numbers are an IP address,” Stern said. “Whoever embedded this watermark wanted to track the distribution of their copies, that’s for sure. But what the heck is that?”
Stern was pointing to another newly revealed part of the watermark. Rainy knew exactly what it was. Even with the colors being off, she could see it clearly. A yin and yang symbol designed to look like a human skull.
“That right there is more than just a watermark,” Rainy said. “That is a calling card.”
Chapter 73
The spray paint was not going to come off. That was Tom’s final conclusion after hours of effort. He’d tried Goop-Off and GoneIt, and two heavy-duty cleaners that the hardware store salesman had recommended. No luck. The paint had set, and he’d have to replace the siding, or paint over it, to get rid of the disgusting words. HEY RAPIST—BRING LINDSEY HOME. That was the message somebody had spray painted three times, in three different colors.
Jill didn’t want to go to school the next day, and Tom wouldn’t have let her go. It wasn’t safe for her in Shilo anymore. She kept to her room for most of the day. She didn’t even come out to eat.
Tom was on the ladder, trying one more application of GoneIt, when Jill shuffled into the backyard through the basement door.
“Hey, honey,” he said, climbing down. “You hungry yet?”
“No.”
Tom checked his watch. “It’s quarter to seven. You haven’t eaten anything all day.”
Jill looked up at the house and recoiled at the sight. “Who would do this?” she asked. “Why won’t they just leave us alone?”
“I’m so sorry about all of this,” Tom said. “But it’ll be all right. You’ll see. Everything is going to turn out just fine.”
“Did you go to the police?” Jill asked.
Tom made a conciliatory expression. “You know I can’t do that,” he said. “Pretty much the whole town is against me at this point. The police most of all.”
“Rainy’s on our side,” said Jill. “Can’t she fix this?” Tom’s face formed a grimace, which Jill noticed right away. “What is it?” she asked.
“Rainy,” Tom said with a sigh. “I should have called her hours ago, but I got so caught up in this vandalism that I forgot.” Tom put his arm around Jill. “I’ll give her a call in a few. Maybe she’ll have some good news to share.”
Tom’s cell phone buzzed in his pocket. He took it out and showed Jill that it was Rainy calling him.
“I guess she beat you to it,” Jill said.
“Hey there,” Tom said into the phone. “I was just about to call you. I’m planning to see Marvin’s parents tonight. They’re sitting shivah at his sister’s house. I was hoping you’d come with me.”
“Tom! Tom! I think we’ve got it.”
“Got what?” he asked.
“Evidence that’ll prove Mitchell Boyd is the distribution source of the images on your laptop. I’m not saying you’re in the clear. But when we put the pressure on him, I bet he’s going to start talking.”
“Rainy, that’s great news. Just great. Where are you now?”
“I’m with Carter. We’re on our way to Shilo to have a little chat with Mitchell Boyd.”
Tom’s phone buzzed again. He was getting another call. He glanced at the number but didn’t recognize the caller. “Rainy, let me call you right back,” he said.