As I suggested in my comment, I wouldn't recommend include pictures of tables. I understand that creating large tables with the tabular environment can be somewhat tedious, but if you are tabulating data files, there is pgfplotstable that can be immensely helpful (it is distributed with PGFplots).
Here's a small example of how it can be used:
\documentclass[border=5,export]{standalone}
\usepackage{pgfplotstable}
\usepackage{booktabs}
\begin{filecontents*}{data.dat}
1. 0. 0.
2. 1.3862943611198906 0.34657359027997264
3. 3.295836866004329 0.1831020481113516
4. 5.545177444479562 0.057762265046662105
5. 8.047189562170502 0.013411982603617503
6. 10.75055681536833 0.0024885548183722988
7. 13.621371043387192 0.0003860932835427209
8. 16.635532333438686 0.000051573450934519735
9. 19.775021196025975 6.054961908444168e-6
10. 23.02585092994046 6.345307244802815e-7
\end{filecontents*}
\begin{document}
\begin{table}
\pgfplotstabletypeset[
columns/0/.style={
column name=\(n\),
},
columns/1/.style={
column name=\(x_{n}\),
fixed, zerofill,
precision=3,
},
columns/2/.style={
column name=\(\Delta x_{n}\),
sci, zerofill,
precision=4,
},
every head row/.style={
before row=\toprule,
after row=\midrule,
},
every last row/.style={
after row=\bottomrule,
},
]{data.dat}
\end{table}
\end{document}
which produces:

If you still wish to include the tables as pictures, then I found this question which is very similar to yours. Assuming that you are only using graphicx and other packages aren't modifying the other environments, then here is how you can fix it:
\documentclass{article}
\usepackage{graphicx}
\begin{document}
\begin{figure}
\begin{minipage}[t][][b]{0.5\textwidth}
\includegraphics[width=\linewidth]{1.png}
\end{minipage}
\begin{minipage}[t][][b]{0.5\textwidth}
\includegraphics[width=\linewidth]{2.png}
\end{minipage}
\begin{minipage}[t][][b]{0.5\textwidth}
\includegraphics[width=\linewidth]{3.png}
\end{minipage}
\begin{minipage}[t][][b]{0.5\textwidth}
\includegraphics[width=\linewidth]{4.png}
\end{minipage}
\end{figure}
\end{document}
with the output being:

pgfplotstable? – JP-Ellis Feb 07 '16 at 01:25\documentclasscommand, has a minimal preamble and then\begin{document}...\end{document}. Unless the problem is a compilation error, the code should compile and be as small as possible to demonstrate your problem. This makes it much easier for people to help you --- and much ore likely that they will! – Feb 07 '16 at 01:44