Thumbnails—those miniature headshots posted on casting websites—are identical to their 8-by-10-inch counterparts. Except, of course, they're smaller. But does that mean they should be treated the same way? Many agents and casting directors say the same standards apply to a thumbnail as to a full-size headshot, but others believe there is a qualitative difference between the two.

Like a regular headshot, a thumbnail has to look exactly like the actor and to "pop," says Jamie Harris, an agent with the Clear Talent Group in New York. But the need to pop is even more critical online, he adds, where a dozen or more thumbnails may appear on a page. They should be in color and feature a full frontal shot of the face. No profiles and no three-quarter shots.

Casting director Dan Cowan, who handles commercials, print, and voiceovers with Broad-Cast in Los Angeles, echoes that view. It's important that the thumbnail be "crystal-clear and 100 percent real," he says. "What you see in the picture should be what you get when you meet the actor. If I'm looking at a thumbnail and questioning what the person looks like, I move on. If there's too much white light, too big a smile, or too much makeup, I move on. Makeup on thumbnails should be very natural." He points out that as tiny as thumbnails are, they are often cropped even further, so clarity is crucial.

L.A. photographer Blake Gardner says a thumbnail focuses on the actor's eyes, and if they're especially beautiful or expressive, that mini-shot can be a useful tool. The thumbnail is also kind to flawed skin, he says, so you don't need the kind of touchups you might with an 8-by-10. But the downside is that you can't see the subject's body, and the small size of the photo may mislead the viewer about the size and shape of the actor. A thumbnail, he adds, is no substitute for a good 8-by-10.

Actor Jessica Gardner (no relation to Blake), who works as a research and casting editor at Back Stage in Los Angeles, fully agrees. Still, because it's relatively cheap to post them online, she sees thumbnails as an opportunity for a little creativity. She has 21 thumbnails on Actors Access, each one wholly real yet each presenting a slightly different persona. At $10 a pop, "I have the luxury of getting some very specific shots," she says. "So when 'Southland' is looking for a nurse co-star, I don't have to submit one where I look all perfectly put together. I can send them one that has me in a T-shirt, no makeup, and my hair pulled back."

But that's not a license to overdo it, she adds: "For my nurse submission, they don't want a pic of me in scrubs wearing a stethoscope. They hate that. There is a fine line. You want to suggest a character or type." In that way, it's just like the standard headshot, but with a little more wiggle room.