This message can be transcluded as part of helping other users. It should be tailored as appropriate.
Hi (name will be substituted), you can find many images available to use on Wikipedia already uploaded by other contributors on Wikimedia Commons. The best way of uploading your own image or video is to go to Commons:Upload and follow the instructions. Uploaded files must be public domain or creative commons with attribution, see the upload page for links to detailed explanations of what these terms mean. Once uploaded to Commons, images can be shown in Wikipedia and any of the sister projects in the normal way (see Wikipedia:Picture tutorial).
Additional points to note...
Logging in - you have to have an account on Commons, this may have already been created under the same name and password as your Wikipedia account, see Special:MergeAccount.
Copyright - if the copyright of the photo is owned by someone else and there is no existing free license to reference (for example on their website), then you need to follow the Commons:OTRS process and confidentially supply an email from the copyright holder. If you think your photo is public domain but want to check the rules that apply then see WP:RFCA and List of countries' copyright length.
Email a photo - see Wikipedia:Contact us/Photo submission. You should note that there may be a long backlog and your email may take days or weeks before getting processed. If you seem technically able, you may get a polite request to do it yourself as this is a low priority for the OTRS volunteers.
EXIF data - image data may be automatically added by the camera or by your photo processing applications. This will be visible after upload so make sure you are happy that the make of camera, when/where it was taken etc. will be consistent with your upload information.
Image verification - the photo can be checked using TinEye after upload, so if it appears on websites which claim 'All rights reserved' or similar then it may get marked for deletion.
A simple standard guide is at Help:Files. If you need more help on getting a suitable photo in the first place, you may find Finding images tutorial helpful. Thanks, ~~~~