- See also: Wiktionary:Images.
It is recommended that all pictures be uploaded to Commons.
Logged in users can set the size of thumbnails they want in special:preferences under "files". The default, used by those not logged in, is 180 pixels. Logged in users can choose from widths of 120px, 150px, 180px, 200px, 250px or 300px.
Also under files in Special:Preferences you can set the size limit of images shown on image description pages. By default, if either the width or the height exceeds 800px or 600px respectively, then the image is reduced in size until it fits within those dimensions. You can choose from sizes of 320x240px, 640x480px, 800x600px, 1024x768px, 1280x1024px, or 10000x10000px. The last will effectively display all images at 100% resolution.
To incorporate your image in an article you need to use the image markup. As an example in its simplest form, to reproduce the photograph at the top of this page you need to insert the following text into an article:
[[Image:Glass-Ball.jpg|thumb|Example image caption]]
Where the image is called Glass-Ball.jpg. "thumb" forces the creation of a thumbnail and you should replace "Example image caption" with a caption.
It gets a bit more complex than this—see w:Wikipedia:Image markup—but the vast majority of images should be displayed in the above format.
Please note that the forced-resizing is discouraged on Wiktionary, as it overrides user preferences. Thumbnails are by default on the right; please do not reposition them on the left or centered. No formal policy exists to specify if they belong at the top of the entry, or closest to where they are defined. For pictures describing English words, they seem to work best when opposite the table of contents (by putting the image wikitext before the first heading.)
An image should usually be placed alongside the definition that it illustrates. If there are too many images in a particular section for this placement to be possible an image gallery may be created that is left-aligned (see A for an example). Galleries are commonly placed at the foot of the Part-of-speech section or in a See also section.