Misguided use of offensive figures in student presentations
Derail the discussion, then re-rail it afterwards.
Keeping the class on topic is useless if students are too uncomfortable to learn.  You are obligated to intervene, once you have learned how to do it.  Here's the method I was taught:

Interrupt.  Example:  &quot;Sorry, I'm interrupting.&quot;
Question.  Example:  &quot;Do you know what stereotype does this image represents?&quot;

The purpose of questioning is to allow someone to indicate that they are ignorant, or to allow themselves to correct an error.  In my experience, students usually realize they did something wrong and correct themselves.

Educate.  Explain why something is offensive/discriminatory/whatever.  Example:  &quot;This image is in a style that was used to depict [identity group] as having [trait].  It is a dishonest message and disrespectful.&quot;

Once the issue is addressed, direct students back to the usual learning activity.

without discouraging the student

Prejudice is inherently discouraging.  Your students can't learn ethical behavior without being discouraged by awareness of unethical behavior.  Hopefully, the &quot;Question&quot; step will at least reduce the hostility of the interaction.