Solved!
EDIT (changed source to Minimal Working Example):
\documentclass{report}
\usepackage{polski}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\graphicspath{ {./obrazki/} }
\usepackage{epstopdf} %eps
\begin{document}
\graphicspath{ {./obrazki/wyniki_eksperymentu/Wyniki przegladu_EMG/wykresy/} }
\begin{figure}[h!]
\centering
\includegraphics[width=10cm, height=10cm]{Najlepszych_30_kombinacji} % Error here
\caption{Najlepsze kombinacje łańcuchów algorytmów ekstrakcji i klasyfikatorów}
\end{figure}
\end{document}
Thank you very much for replies. I was so fixed on underscores problem, that i didn't noticed white space in dir path :D
Since i can't give you any reward (only comments - no answers) :
"Best Answer Award" goes to Henri Menke for package which solves problem:
\usepackage{grffile}
Second award goes to cfr for spotting source of the problem :)
-works just as well, and is easier to type. But if you can't or would rather not, try escaping the underscores:\_. I haven't tested this, but it's worth a shot. – Sean Allred Jan 03 '14 at 03:38grffilepackage by Heiko Oberdiek fixes many problems regarding inclusion of graphics, such as utf-8 encoded file names of multiple dots in file names. – Henri Menke Jan 03 '14 at 07:54