This kind of website publication information will often be found at the bottom of the home landing page:
For images accessed online: "Provide the artist's name, the work of art italicized, the date of creation, the institution and city where the work is housed. Follow this initial entry with the name of the Website in italics and the date of access.
If the work is cited on the web only, then provide the name of the artist, the title of the work, and then follow the citation format for a website. If the work is posted via a username, use that username for the author." (Purdue OWL)
Example:
Wright, Frank Lloyd. Sprite Statue. 1913. Arizona Biltmore, Phoenix, Arizona, USA. Artstor, library.artstor.org/#/asset/CANYONLIGHTS_DB_10312430638. Accessed on 1 Aug. 2016.
NOTE: You must list your date of access, because web pages are often updated. Use "n.d." if there is no publishing date and/or "n.p." if no publisher name.
Editor, author, or compiler name (if available). Name of site. Version number, Name of publisher/organization/institution affiliated with the site, date of resource creation (if available), URL, DOI or permalink. Date of access (if applicable).
Example:
The Purdue OWL Family of Sites. The Writing Lab and OWL at Perdue and Perdue U, 2008, owl.english.purdue.edu/owl. 2016 - 2017.
This also happens to be the citation for this Lib Guide!
For an individual page of a website, as with an entire website, it is still appropriate to include the author or editor (if known), and the title of the page. If there is a title to the page, list it in quotation; if the title of the page is the same as the publisher or sponsor, you only need to list it once, in italics.
Example:
Gaworecki, Mike. "How 'due diligence' is helping curb the illegal timber trade in key markets." Mongabay, 12 May 2016, news.mongabay.com/2016/05/due-diligence-helping-curb-illegal-timber-trade-key-markets/. Accessed on 16 May 2016.