Once you’ve uploaded an image to the Commons, adding it to a Wikipedia article is very simple. You just go to the article, click “edit this page,” decide where you want the image to be, and type a link to the image page. It’ll look something like this: [[Image:Nameofimage.ext|some other optional stuff]]. (More on the “other optional stuff” in a moment.) Add an edit summary, do a quick preview, and save the page.
The software assumes that the image name you add to an article refers to one at the English Wikipedia, if one exists there. If the English Wikipedia doesn’t have an image with that name, the software looks at the Commons. That’s another good reason to name an image at the Commons in such detail that it’s unlikely you’ll accidentally choose one that already exists at the English Wikipedia. (No, the software won’t warn you.)
Note
Forgot the name of that image that you uploaded to the Commons? Don’t worry. Just sign in, click the “my contributions” link in the upper-right, and look at the names of the image files you’ve created. You can do the same at the English Wikipedia, if you’ve uploaded images to that site. Filter out everything but image pages by changing the Namespace field to Image.
When there is more than one image in an article, spread the images evenly within that article. Each image should be relevant to the section it is in, and normally there should be only one image per section.
For accessibility and other reasons, you should put an image inside the section it belongs to, after any “Main” or “See also” template at the top of the section. The more general rule is to put an image immediately above the paragraph of text to which it most closely belongs. It’s certainly okay to have text following the image, within the section where it’s placed.
Multiple images within a single section, while not forbidden, can cause problems, particularly if the section is short. In particular, don’t place an image on the left side of a section and a second image directly opposite, on the right side. For some readers, this squeezes text into a tiny column between the two images. On some computer screens the images may even overlap. (Even if you know how to use special parameters in the image links to force blank space between the images to avoid squeezing the text, don’t do it. The blank text looks terrible on larger computer screens.)
Note
What you see on your screen isn’t the same as what other readers see: Both screen sizes and resolutions (dots per inch) vary widely. Wikipedia is intended for readers everywhere in the world, many who have older computers with smaller screens. So, if you’ve got a wide, high-resolution screen, enjoy it, but don’t fall into the trap of thinking that what looks fine on your screen will look fine on everyone else’s.
Some editors prefer to put all images on the right side of an article, aligned with any info boxes. Other editors prefer them to be evenly alternated between left and right (for example, one image on the left in one section, and the next image, in a following section, on the right). Either approach is acceptable, but don’t get into ownership issues over the arrangement of images—aesthetic judgments are inherently subjective, and not worth fighting about.
Note
One place that’s bad for an image is left-aligned immediately under a subheading. The heading ends up directly above the image (making it look somewhat like a label) and puts the subsection text to the right of the image, disconnecting it from the heading. If you want an image left-aligned in a subsection, make sure there is at least a paragraph of text between the image and the subheading. If you absolutely want the image to follow directly after a subsection heading, right-align it.
You control the alignment of images by typing instructions into the wikitext for the link. The next section tells all.
Once you decide in what section you want an image to appear, and where within that section, you simply place a link to the image within the wikitext. At its simplest, this would be [[Image:Nameofimage.ext]]. But you almost never find such a simple image link in an article, because it plops the image, at full size, wherever the image link appears in the wikitext, even if that’s in the middle of the screen. Nor, with this simple link, will text flow around the image. So don’t create image links like this one, and if you see one, fix it.
The way that you control how an image appears is to specify various options. Here’s a common specification: [[Image:Nameofimage.ext | thumb | 200px | right | caption text]]. Here’s what the details of the options mean:
Thumb. Displays the image as a small thumbnail. The image isn’t shown full size (the reader can click the image to get to a full-size version). The image has a gray frame around it and a caption (if you specify one as described in the fourth bullet). If you don’t specify either “thumb” or (less commonly used) “frame” as an option, then any caption you include won’t be visible to readers.
Note
These options are case sensitive, so don’t type Thumb, Right, and so on.
200px. Determines the width of the thumbnail image in pixels. On a screen with 600 by 800 pixel resolution, 200px means that the photo takes up one-quarter of the width of the screen. If you don’t specify a size, the default is 180 pixels. Wikipedia:Extended image syntax (shortcut WP:EIS) recommends not specifying a size, so that the reader’s preferences determine whether the displayed size is 180 pixels or something larger or smaller.
Tip
If you’ve got a particularly big or particularly small screen, you can tell Wikipedia how you personally want to see thumbnails displayed on your screen. Click My Preferences, then the Files tab, and then select from one of the six sizes (120px to 300px). After you click Save, all thumbnails you see in Wikipedia will be that size, except where an editor has specified an exact size.
Right, left. The image appears all the way to the right (left) of the screen. Right is the default setting, so you don’t have to type it if you don’t want to.
Caption text. The caption should provide useful information. In an article about New York City, for example, an image with the caption “New York City” isn’t helpful, while something like “Panorama from the top of the Empire State Building” is much more useful. (You’ll find great advice about writing captions at the guideline Wikipedia:Captions; the shortcut is WP:CAP.)
Caption text always comes last in an image link. All the other options (thumb or no, size, align right or left) can be in any sequence. And the caption must start with a capital letter.
For more image syntax, see the pages Help:Images and other uploaded files (shortcut: H:IOUF) and Wikipedia:Photo tutorial (shortcut: WP:PIC).
In some articles, a lot of images are useful—for example, the article Great Wall of China. But you don’t want to put images into sections where they don’t really belong just because that’s the only place you can think of. Instead, you can put a gallery at the end of an article, with lots of images for the reader to see. That way, the images don’t get in the way of the content of the article, but they’re available to the reader.
The wikicode for creating a standard gallery is very simple; here’s an example with three images (and made-up image filenames):
<gallery> Image:Firstphoto.jpg Image:Secondphoto.jpg | Caption for second image Image:Thirdphoto.jpg </gallery>
You can have captions on all images, of course, and aren’t limited to JPEG images. The page Wikipedia:Gallery tag (shortcut: WP:GALLERY) has full details.