Encoding information in temporal chaotic signals and decoding it via chaotic synchronization between transmitter and receiver constitute nowadays a well-established technique. The method has been successfully implemented in electronic and optical systems. The latter, besides offering high speed of information transfer, provide a natural way of spatiotemporal communication through the use of broad chaotic optical wavefronts. An optical setup for spatiotemporal chaotic communications was recently proposed based on nonlinear ring cavities. In this article, we examine further in detail such a proposal, comparing two different encoding methods, namely injection and modulation. In the two cases, the correlation between input, transmitted, and output signals is estimated by means of measures taken from information theory. The influence of the message amplitude and parameter mismatch is analyzed.