Chess.com has provided an intuitive and self-explanatory procedure ...

MY HOME, Photos, Create a photo album.

Supply a name for the album and a description. Click on SELECT PHOTOS.

Click on CLICK HERE TO UPLOAD PHOTOS.

Select one or more photos. Click Open.   - depends on which OS you are using.

Click on UPLOAD MORE PHOTOS or SAVE & CONTINUE.

This album is currently not published. You must click the "Update & Publish" button below to allow others to view your photos.

Click on UPDATE & PUBLISH.

You're done!

Rael, TheGrobe et al have provided detailed instructions here  (http://www.chess.com/forum/view/help-support/screenshots) on editing images and using them in forum posts.