10 Image #CaptionTips from a transcriptionist:

1. Any words are better than nothing.
2. You don't need to say it's "a picture of…" screen readers will already say it's an image.
3. Start with the framing or format (i.e. close up, landscape, meme, text).
4. Think about the reason you're posting the pic and describe that first, add background details if you have time.
5. Pretend you're talking to someone on the phone and want to tell them about this cool thing you're looking at.
6. Transcribe any and all text in the image, even if it's the only thing you do.
7. If you've described the image in your post, you don't need to copy and paste it again in the caption. But again, don't leave it blank, just put something like "as described."
8. You can add small subjective notes, but don't give too much interpretation of the image in your own opinion.
9. Caption jokes are fun, as long as they still describe the image objectively.
10. Use punctuation, and capitalize words properly. A lot of us have interacted with this tech when calling customer service or talking to Siri, so keep in mind that you're writing for a computer to read, and it needs all the help it can get.