Images I use in class tend to be as simple as possible. A quick sketch in the students’ notes or on the board. In other words, they serve a purpose rather than act as decorative “fluff”.
Of course, you should decide for yourself what’s appropriate for your group. Many of the images here might not work for adults and are better suited for kids. I encourage you to use a mix of styles to maintain interest and fun.
You can always reach me with ideas or feedback at: firstname.lastname@example.org
When practicing letters, look out for strange fonts. Young learners only need lines and circles to make clear letters but if the lines and circles don’t line up uniformly, kids can get confused. The “Primer Print” font is generally good but drops the ball when it comes to the letter “A” as it doesn’t actually line up with the middle guide lines. I’ve corrected that manually in my materials.