Trying to Write on image

Question

I was trying to edit a diagram and add a dimension line , as you see in the attached image,but I could not reach the arrows appropriate to draw the same arrow, if it's possible to do that in Latex , I have no Idea how to, could someone help me ? I am reading these links : here and here but still I don't get it how I can draw a straight line and ...

I have tried for the code so far I can not draw the arrow with two heads, it appears only one head in one end of the middle like beside which you see the letter f , I still don't know how to write the letter beside the line:

\documentclass[11pt,a4paper,twoside,openright]{report}
\usepackage{tikz}
\usetikzlibrary{calc,intersections,through,backgrounds}
\begin{document}
\begin{tikzpicture}[--, thick]
\draw  (-10,0) -- (-9,1);
\draw  (-9,1) -- (-7.5,1);
\draw  (-7.5,1) -- (-6.5,0);
\draw  (-6.5,0) -- (-5.5,-1);
\draw  (-5.5,-1)-- (-4,-1);
\draw  (-4,-1)-- (-3,0);
%dimensions
\draw  [|<->|] (-8.25,0) -- (-8.25,1);
\draw  [|<->|] (-10,-0.5) -- (-6.5,-0.5);
\begin{scope}[dash pattern=on 2pt off 3pt on 4pt off 4pt];
\draw[dashed] (-6.5pt,0pt) -- (-6.5pt,-1pt);
\end{scope}
\begin{scope}[ultra thick]
\draw [->] (-10.5,0) -- (-1.5,0);
\draw [->] (-10,-1.5) -- (-10,1.5);
\end{scope}
\end{tikzpicture}
\end{document}

Answer 1

This demonstrates how to add labels to lines and how to get the dashed line in the right place. Note that (6.5pt,0.5pt) is not generally the same as (6.5,0.5)! I've also simplified your path specification a bit and removed the non-working option to tikzpicture.

• midway puts the label halfway, which is wanted for the f and c.
• pos=.95 puts the label 95% of the way to the end point, which is wanted for the labels on the axes.
• left and below specify the relative position of the label with respect to the line.

Code

\documentclass[tikz,border=10pt]{standalone}
\begin{document}
\begin{tikzpicture}[thick]
    \draw  (-10,0) -- (-9,1)  -- (-7.5,1) -- (-6.5,0)  -- (-5.5,-1) -- (-4,-1) -- (-3,0);
    %dimensions
    \draw  [<->] (-8.25,0) -- (-8.25,1) node [midway, right] {$f$};
    \draw  [<->] (-10,-0.5) -- (-6.5,-0.5) node [midway, below] {$c$};
    \draw [dashed] (-6.5,0) -- (-6.5,-.75);
    \begin{scope}[ultra thick]
      \draw [->] (-10.5,0) -- (-1.5,0) node [pos=.95, below] {$x$};
      \draw [->] (-10,-1.5) -- (-10,1.5) node [pos=.95, left] {$y$};
    \end{scope}
\end{tikzpicture}
\end{document}

Answer 2

JPEG is a quite worse format for drawings. Therefore it is better to redraw the image. The following example uses TikZ. The function is strictly drawn using the parameters f, c, α (\fHeight, \cWidth, \alphaAngle).

\documentclass{article}
%\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{bending}
\pagestyle{empty}

\begin{document}
  \setlength{\unitlength}{.5mm}
  \begin{tikzpicture}[
    x=\unitlength,
    y=\unitlength,
    >=Triangle,
  ]
    \def\fHeight{17}
    \def\cWidth{50}
    \def\alphaAngle{45}
    \def\alphaRadius{14}
    % Image as background as help for redrawing
    % \node[
    %   inner sep=0pt,
    %   above right,
    % ] at (-16.25, -20.75)
    %   {\includegraphics[width=150\unitlength]{QpYZE.jpg}}
    % ;

    % Coordinate axes
    \begin{scope}[
      thick,
      ->,
    ]
      \draw (-9, 0) -- (125, 0) node[below left, xshift=-.5em] {$x$};
      \draw (0, -20) -- (0, 30) node[below left, yshift=-.25em] {$z$};
    \end{scope}

    % Function
    \pgfmathsetmacro{\xf}{\fHeight * cot(\alphaAngle)}
    \draw[
      semithick,
    ]
      (0, 0)
      -- (\xf, \fHeight) coordinate (A)
      -- (\cWidth - \xf, \fHeight) coordinate (B)
      -- (\cWidth + \xf, -\fHeight)
      -- (2*\cWidth - \xf, -\fHeight)
      -- (2*\cWidth, 0)
    ;

    % Annotations
    \begin{scope}[
      thin,
      <->,
      shorten <=.4pt,
    ]
      \draw[shorten >=.3pt]
        (\cWidth/2, 0) -- node[right] {$f$} ++(0, \fHeight)
      ;
      \draw[shorten >=.2pt]
        (0, -6) -- node[below] (c) {$c$} ++(\cWidth, 0)
      ;
      \draw[shorten <=.2pt, shorten >=.2pt]
        (\xf, \fHeight + 4) -- node[above] (cp) {$c_p$}
        (\cWidth - \xf, \fHeight + 4)
      ;
      \draw[shorten >=.3pt, radius=\alphaRadius]
        (\alphaRadius, 0) arc[start angle=0, end angle=\alphaAngle]
      ;
      \node at (\alphaAngle/2:.65*\alphaRadius) {$\alpha$};
    \end{scope}

    % Help lines
    \draw[thin, densely dashed]
      (\cWidth, 0) -- (\cWidth, 0 |- c.south)
      (A) -- (A |- cp.north)
      (B) -- (B |- cp.north)
    ;
  \end{tikzpicture}
\end{document}