May I publish the slides from my presentation that use figures from published papers as examples?
Yes, it is legal to reproduce and legal to use exact figure if it is not copyrighted.

If you refer to the source, you can reproduce the data. Which means you cannot use the figure by taking a screenshot, but rather reproduce the result by yourself. Data and equations are not copyrighted. 

If the article is in open science or creative commons license (most of them are nowadays) you can take screenshots and use them. 

To avoid complications, why not make your own figure of the data? It is pretty simple. After taking a screenshot, using plot digitizer you can get the data. Use your own plotting tool to make the picture.  This is a problem if your picture is an image from the experiment. Then you need to obtain permission to use that image.