One of the things that I often do to spark students' curiosities and questions about a topic is to present them in an interesting image. To allow students to comment directly on the image I will put it into ThingLink then embed the ThingLink image into a blog post. See the example below.
By using ThingLink in this way I can have students and more than just text comments in response to the visual prompt. To extend the activity I can have students look for YouTube videos and or websites that will help to explain answers to the questions generated by looking at the featured image.
Helpful guides to using ThingLink in your classroom.
Thinglink Edu - Your Students Can Use Thinglink Without Email Addresses, Here's How
How to Embed Interactive ThingLink Images Into a Blog Post
ThingLink Remix - Share One Image and Let Your Whole Class Make It Interactive