I'm trying to get a burndown widget image, and I want to know if there's a possibility to get this through REST API.
I tried using this one:
but I'm not sure if this chart image and the burndown widget are the same.
The Rest API you mentioned in description is used to get the Sprint Burndown chart of the Team Iteration.
GET https://dev.azure.com/{organization}/{project}/{team}/_apis/work/iterations/{iterationId}/chartimages/{name}?api-version=7.1-preview.1
If the burndown widget you mentioned is the Sprint Burndown widget, you can use this Rest API to obtain it.
But if you want to get the Burndown widget, I am afraid that there is no out-of-box Rest API can get the Burndown chart image for the time being.
Here are the screenshots of the Burndown and Sprint Burndown widgets:
I can fully understand your requirement. You can submit a suggest ticket in the site: Developer Community to report this feature.