For guidance on this subject, you might consult the QuickSheet "Citing Ancestry Databases & Images." This four-page laminated publication, by Elizabeth Shown Mills, is available for $12.19 at Amazon.
Page 3, under the header "Family Trees," describes how to cite "Personal data, noting source or lack of it," and "Photos or documents" from member family trees at Ancestry. I use this publication all the time as a quick guide to citing sources at Ancestry.
Another excellent reference, also by Elizabeth Shown Mills, is Evidence Explained: Citing History Sources from Artifacts too Cyberspace.