Warning: a possible image without description

Question

I employ TexLive 2017. I use the following piece of codes in my tex.

\begin{figure}[t]
\centering
\begin{subfigure}{0.45\columnwidth}
\epsfig{file=fig/a.eps, width=1.0\columnwidth}
\caption{a}
\end{subfigure}
\begin{subfigure}{0.45\columnwidth}
\epsfig{file=fig/b.eps, width=1.0\columnwidth}
\caption{b}
\end{subfigure}
\vspace*{-5pt}
\caption{\bf a versus b}
\end{figure}

It leads to a warning, which complains "A possible image without description on input line ...". I wonder why this warning happens.

Answer 1

From the warning you quoted, I assume that you use the acmart document clss.

To quote from the manual of version 1.56:

2.6 Descriptions of images Blockquote

Some readers of ACM publications might be visually challenged. These readers might use a voice-over software to read aloud the papers. It is important to provided them a description of each image used in the paper. The command \Description[<short description>]{<long description>} should be placed inside every figure , teaserfigure or marginfigure environment to provide a description of the image(s) used in the figure. Unlike \caption , which is used along- side the image, \Description is intended to be used instead of the image [...] At present the lack of descriptions generates a warning at compilation.