When using the ACS style, there are different rules depending on whether you're describing and citing an image/figure in-text or if you are reprinting an image/figure in your paper. Each scenario requires different information.
REPRINTING AN IMAGE/FIGURE:
When you are reprinting an image or figure in your paper, you need to ensure you have the approval to do so. In addition, you need to ensure that you're including an image or figure caption that indicates that you have received approval from the copyright holder to reprint it in your paper. This page will not cover the details of this - if you need further support in asking for permission to reprint and image/figure, please contact your subject librarian or the Copyright Office.
MENTIONING/DESCRIBING AN IMAGE/FIGURE:
Alternatively, if you are only describing or making reference to an image or figure, and are not reprinting it, then you can cite the image as coming from the item it was printed it - the journal article, the book, etc. See below for more information.
When mentioning or describing and image or figure in your paper, you can incorporate the citation for the full source it came from - instead of simply citing it as an image.
As Li, Wang, Wu, Liu, Bo, and Ceder detail in Figure 1¹, JT activity is...
1. Li, X.; Wang, Y.; Wu, D.; Bo, S.-H.; Ceder, G. Jahn-Teller Assisted Na Diffusion for High Performance Na Ion Batteries. Chem. Mater. 2016, 28 (18), 6575-6583. DOI: 10.1021/acs.chemmater.6b02440