Background pattern for equations (to defeat PhotoMath)

Question

I'm a math teacher and I'm dealing with the problem of doing math tests with my students at home. I recently found out that there are certain background patterns that can prevent apps like PhotoMath to read math equations/problems (you can see an example in Edia website) and I'd like to implement something like that in LaTeX. To be clear, I'd like some variation of the equation ambient which automatically add said background and change the text colour. I have an image of the pattern I'd like to use (see below), but I don't know where to start. I'm not asking for a code solution, I ask you to kindly point me to the right direction: which package(s) should I use? is it better to build the pattern within LaTeX or is it possible to use the image directly?

Thank you for your kind reply. I will edit this post with a MWE as soon as i will be able to produce one.

My answer here may give some ideas...https://tex.stackexchange.com/questions/237520/security-printing-in-pdflatex-documents/237526#237526 — Steven B. Segletes, Mar 12 '21 at 00:01
Yes, I know there are powerful alternatives to PhotoMath... I try my best: if a student want to cheat he/she will find a way. At least it won't be the super easy and accessibile one. — mattinodigitale, Mar 14 '21 at 07:48

score 5 · Accepted Answer · answered Mar 11 '21 at 23:07

You can use the combination of tcolorbox and empheq. Here is an example in which I am probably overdoing it a bit, but it is easier to drop options than to add them.

\documentclass{article}
\usepackage[skins,theorems]{tcolorbox}
\usetikzlibrary{patterns.meta}
\usepackage{empheq}
\newcommand{\diff}{\mathop{}\!\mathrm{d}}
\newtcbox{\otherbox}[1][]{nobeforeafter,math upper,tcbox raise base,
enhanced,frame hidden,boxrule=0pt,interior style={top color=green!10!white,
bottom color=green!10!white,middle color=green!50!yellow,
postaction={pattern={Hatch[angle=45,distance={3pt/sqrt(2)},xshift=.1pt]}, 
pattern color=blue}}, fuzzy halo=1pt with
green,#1}
\begin{document}
\begin{empheq}[box=\otherbox]{align} a&=\sin(z)\\
E&=mc^2 + \int_a^b x\diff x
\end{empheq}
\end{document}

Your suggestion works incredibly well!! Thank you very much: I will try to adjust the colours, but this works just fine! :) — mattinodigitale, Mar 12 '21 at 08:54

score 1 · Answer 2 · answered Mar 13 '21 at 22:21

I want to thank user237299 again for his/her brilliant suggestions! Here is my (little) editing of his work, hoping that someone will find it useful.

I don't know how to "embed" the \color{yellow} command into the environment (it need to be repeated). I created a simple command for in text equations (like with single $), which can be used for example to list some exercises into an enumerate environment.

If you prefer the equation numbering on the left you need to add [leqno] after documentclass, as said here.

\documentclass{article}
\usepackage{xcolor}
\usepackage[skins,theorems]{tcolorbox}
\usetikzlibrary{patterns.meta}
\usepackage{empheq}
\newcommand{\diff}{\mathop{}!\mathrm{d}}
\newtcbox{\antiphotomathbox}[1][]{nobeforeafter, math upper, tcbox raise base, enhanced,    frame hidden, boxrule=0pt, interior style={
        top color=gray,bottom color=gray,middle color=gray,
        postaction={pattern={Hatch[angle=45,distance={10pt/sqrt(2)},xshift=.1pt]}, 
            pattern color=gray!80!black}}, fuzzy halo=1pt with gray,#1}
\newcommand{\antipm}[1]{\antiphotomathbox{\color{yellow}#1}}
\begin{document}
Solve the following equations without the help of PhotoMath:


{\begin{empheq}[box=\antiphotomathbox]{align*} 
        &\color{yellow} x^2-5x+11=0\
        &\color{yellow}x^2-12x+15=0\
        &\color{yellow}x^2-3x+19=0
\end{empheq}}
\begin{empheq}[box=\antiphotomathbox]{align}  \color{yellow}x^2-12x+15=0
\end{empheq}
Calculate the following integrals without the help of PhotoMath:
\begin{enumerate}
    \item $\antipm{\int_{2}^{3}x^2-3x-4 dx}$
    \item $\antipm{\int_{3}^{4}x^2-4x-5 dx}$
    \item $\antipm{\int_{4}^{5}x^2-5x-6 dx}$
\end{enumerate}
\end{document}

Background pattern for equations (to defeat PhotoMath)

2 Answers2