There are lots of ways to style an image. You can adjust its size, position it on the page, give it a border, a caption, a background color, and more.
Here's a simple tool for dressing up an image, so it shares a layout similar to other images on the site. Paste this code into your wiki-text:
|web-address of an image, or substitute | flickr-ID=
(optional) a dimension, like 300px or 20em
(optional) style the image, turn it into a link
(optional) flickr images are captioned automatically, unless specified here
(optional) position the textbox (float:right, margin:0, etc)
— Make sure there's no space after the closing double brackets.
All you really need is to specify img-source or flickr-ID. The rest is optional. For instance, here's the code that lays out the image above, pulls the flickr title and credits the photographer:
For more background about images, here's a more in-depth how-to.