Here’s my humble attempt at creating a guide for clients on how they can select image material that’ll keep their designers both happy and effective. It should also be useful for illustrators and photographers and other people who like printing things. It’s supposed to be educational, so if you have questions, comments or corrections, please post them below.
The two most important rules to remember when finding images are:
- you need to be legally allowed to use the images
- you need enough pixels to print them the right size (unless they’re vector images)
Let’s take them in order:
1: finding images you are allowed to use
Unless anything else is specified, you can assume that any image you find online is copyrighted. This means you can’t use it without the permission of the owner of the copyright, usually the creator.
When in doubt, ask, if you can’t ask, don’t use the image.
Sometimes the creator will respond to your attempts at contacting them, sometimes there’s no way to even figure out who they are. This is why Google Image Search is usually a bad way of finding images for non-private use.
There’s hope, though! You could always hire an illustrator or a photographer, if that seems a bit much there are both cheap and expensive stock photo sites out there. In fact there are even sites with free stock photos.
Either way, always take care to read the license, because you’re rarely allowed full rights to use the image however you want. Another option is to use images that are in the public domain.
Check the end of the post for more on where you can find images.
2: checking if your image has enough pixels
Most images that are in a digital format are stored as pixels – that is, as (usually square) blocks of different colors. A computer display will usually show the pixels one by one, each set of red-green-blue lights showing one pixel each – printing doesn’t work that way, and you’ll almost always need more pixels to show an image in print the same size as you can show it on your display – unless you want it to look blurred or pixelated.
If you want to be 100 percent sure that your picture has enough pixels, all you have to remember is that you need 300 pixels per inch (ppi), or about 120 pixels per centimeter. So if you’re printing an image at 10 by 15 centimeters, the image has to be at least 1200 pixels wide and 1800 pixels tall.
There are many ways to find out how many pixels an image has, in Firefox, right click the full-size image, and click View Image Info. In windows 7, right click the icon and select Properties, go to the Details tab and look for Dimensions. Ignore whatever it says about resolution.
An A4 piece of paper is 21 centimeters wide, and about 30 centimeters tall – so you’d need your image to be at least about 2500px wide and 3600px tall. Try to figure out the same numbers for the size you expect your image to be printed at, round up to numbers that are easy to divide by, and math your way to what you need. You don’t need to be completely exact.
As long as you’re above 300 ppi, you are very safe – except for the special case of one bit color images: in that case, try to get 1200 ppi. A one bit color image, is an image that has only two colors (usually black and white). With no intermediary colors to smooth them out, the edges will look jagged up close. Click this image to see:
Sometimes, though, you don’t need to worry about pixels at all…
From the Wikipedia article: Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical equations, to represent images in computer graphics.
This means that a computer can render a vector image at any size without it looking blocky. Vector images are usually either stored as AI, EPS or PDF-files. If you have a file in one of the above formats, and you’re unsure if it’s a vector image, open it in Adobe Reader and zoom in as far as you can – if it doesn’t look blocky, it’s probably a vector image.
Professionally made logos almost always exist in a vector format (just make sure you find the right file), photographs never do.
where to find images
Obviously there are your standard stock photo sites where you can find and buy images. If your budget can handle it, Getty Images and Corbis are the giants in the field – but there’s also a plethora of smaller and less expensive sites like SXH and Istockphoto.
SXH lets their photographers offer up their images for free as well – just take care to read the brief “Availability” note next to the download button. Morguefile is another good site for free royalty free images. In fact, the image above is from Morguefile (user: procrastinator) and the photo of the pixels is from SXH (user: vincitrice).
But the biggest source of images you can use is an advanced Flickr search for images with a creative commons license. Creative Commons licenses have been designed by an American non-profit corporation to make Copyright more flexible. From the Wikipedia article:
- Attribution: Licensees may copy, distribute, display and perform the work and make derivative works based on it only if they give the author or licensor the credits in the manner specified by these.
- Non-commercial: Licensees may copy, distribute, display, and perform the work and make derivative works based on it only for noncommercial purposes.
- No Derivative Works: Licensees may copy, distribute, display and perform only verbatim copies of the work, not derivative works based on it.
- Share-alike: Licensees may distribute derivative works only under a license identical to the license that governs the original work. (See also copyleft.)
Mixing and matching these conditions produces sixteen possible combinations, of which eleven are valid Creative Commons licenses and five are not.
Wikimedia Commons is probably the biggest place to find photos and illustrations that are in the public domain, but there are lots of smaller sites with old pictures and illustrations. Have fun searching!