Captions of floats (figures and tables) in LaTeX are by default typeset the same way as the body text. For better readability it could be appropriate to use a different font, font size or margin for the captions. This is possible with the LaTeX package caption.

For example, with the following addition to the document preamble:

\usepackage[font=sf, labelfont={sf,bf}, margin=1cm]{caption}

your captions will look as follows: the caption in a sans serif font (font=sf), label in bold (labelfont={sf,bf}) and more margin on the left and right (margin=1cm). Like so:

customized caption

More information in the documentation of the caption package.