You can use knitr::include_graphics()
as this one accepts a vector of paths as an argument.
Then you should use fig.show='hold',fig.align='center'
in order to plot them on the same line and out.width="49%", out.height="20%"
to control the output size.
```{r, echo=FALSE,out.width="49%",
out.height="20%",fig.cap="caption",fig.show='hold',fig.align='center'}
knitr::include_graphics(c("path/to/img1","path/to/img1"))
```
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