Help:Introduction to images with VisualEditor/4
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Introduction
Adding images to Wikipedia
Uploading images
Wikimedia Commons
Inserting images
Worth a thousand words
Editing the details
What am I looking at?
Galleries
For large picture sets
Summary
Review of what you've learned

A good caption explains the image so that readers understand what they're looking at.
Alternative text is used to describe the contents of an image for users who can't see it.

The "Advanced settings" window contains various additional parameters. These include the alignment, the type, and size of the image. It is usually best to leave the defaults, but sometimes a larger image may be more useful.