How to convert text/listing into images

Question

I would like to ask is there any way to covert some texts/listings to images so that they could not be copied?

I would appreciate any suggestions.

Answer 1

Matt G answered another question

You can use ImageMagick to convert the pdf to an image pdf. Running convert file1.pdf file2.pdf will create a pdf called file2.pdf which is about the same size as the input pdf but since its an image, the text cannot be selected. There is a notable decrease in quality though

To improve quality simply add a high density (eg 300):

convert -density 300 file1.pdf file2.pdf

an example:

\documentclass[htb]{memoir}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{duckuments}
\usepackage{lipsum}
\begin{document}
\blindduck
\lipsum[1-20]
\end{document}

produces the markable text:

and can be converted to high quality pictures:

You can increase the density to above 300, if it was not enough

Edit: unobtainable text

If your goal is not merely to turn the text into a picture, but make it unobtainable, you can make it the same color as the background:

\documentclass[htb]{memoir}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{xcolor}
\usepackage{duckuments}
\usepackage{lipsum}
\begin{document}
\textcolor{white}{
\blindduck}
\lipsum[1-20]
\end{document}

Produces a pdf with markable text:

Converting it will make it both unmarkable and invisible, so you cannot obtain it from the pdf:

using the tool posted by @KJO on the above image I got the text:

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, adipiscing vitae, fells. Curabitur dictum

Leaving the duck completely out.