I am trying to embed an image in a pdf so that when you open the pdf in acrobat or another reader the image is correctly tagged as an image and there is alternative text. So far I am able to export the back end tags so that I can see tags on tables and paragraphs, but the image comes through tagged as a paragraph and I am unable to add any alternative text. This is the code I am using: 

\externalfigure[district.pdf][height=10cm]