How to I specify the size of an image in LaTeX?

In order to use a figure on writeLaTeX, you first have to upload it via the project menu. You can then specify the size of the image in the output document using the options to the includegraphics command:


There's an example of this in our default paper template - simply click to create a new paper and see how the image 'frog.jpg' is set to half the text width.