Hey @JamesCutler!
I have an idea, but it may not be what you want. Any time I can do something in Canvas, I try to use Canvas tools and features when at all possible. This way, I do not need to worry about third party vendors changing Terms of Service, or charging for what used to be free. And when you can add a bit of fun "magic", it helps too.
In the image below, I have a basic example where I added my own images and definitions. I used a four row table, but the table could be any configuration you want. The first and third rows are where the images are placed in each column. The second and fourth row contain the words and definitions in each column. The magic comes into play because the cell background and the text of rows two and four are black which hides the text. Triple clicking in the black area, will select and highlight all of the text within a paragraph. Because the highlight color of the selected text is different than the text or the background colors, the text becomes visible. To hide it again, just click somewhere else on the page to deselect the text.
The text under the image of the horse is visible because it is selected.
While this method definitely does not have ads, it does not include the tracking to see how well the students do. However, you could use a Canvas Quiz with same or similar images as a pretest prior to publishing the page with the flash cards. Once the students have studied the flashcards, they could take the quiz again as a post assessment. Post assessment could be taken for a grade or not, depending on your preferences.
Just a thought. Let me know if you have any questions.
