Assume I have a screenshot in png format and make a copy of it in eps format by using ImageMagick.
I create two input file, namely
ForPNG.tex imports the png image and is compiled by pdflatex.
ForEPS.tex imports the eps image and is compiled by latex-dvips-ps2pdf.
The question is, which one produces the smaller pdf file in size?
In my experience,
ForEPS.pdf will be smaller than
ForPNG.pdf. But I am not sure whether it is a summary.