Wikipedia:Manual of Style/Images
Wikipedia contains many thousands of images, There are photographs, drawings, diagrams, maps and even works of art (see Wikipedia:list of images for galleries of public domain or otherwise freely redistributable images organized by category). Many of these images are photographs taken by Wikipedians, others are found on the Net. Whatever the source, before you upload any image make sure you read the image use policy.
Once you have uploaded your image there is a little housekeeping to be done. You should edit the description page and make sure the copyright status of the image is clearly stated. To simplify this you might consider using one of these copyright tags.
To incorporate your image in an article you need to use the image markup. And remember those who use the alternate text. (You can also use the legacy markup guidelines if the need arises.) Be sure to write a good caption for your new image.
Eventually some of the images reach the end of their life cycle. They may be superseded or replaced by an image with a friendlier copyright policy. If you come across an image that needs to go then list it on Wikipedia:Images for deletion.
If you're looking for an image, check public domain image resources and Google images with "site:.us OR site:.gov OR site:.mil" and check to see if the images you find are public domain. Failing that, you might list it on Wikipedia:Requested pictures so that another contributor might find or create a suitable image.
If you have contributed or found an image that stands out from the crowd, you are invited to nominate it for inclusion on the Wikipedia:Featured pictures list.