Pressgram has built-in support for publishing links to your images (and associated blog posts) to Facebook and Twitter social networks. But what if you prefer the App Developer Network? There are two solutions that I've used that seem to work but both involve publishing your photo a WordPress blog first.
If This Then That (IFTTT) is a service that lets you connect various online services (channels) and do actions based on simple rules triggered by actions. The combination of online service and rule is called a recipe. I created a IFTTT recipe to push links from my WordPress blog that have been tagged "#pressgram-photo" to my app.net stream. When I want to post my Pressgram image to ADN, I follow the same procedure that I would for posting to my WordPress blog but I add the tag "pressgram-photo' to the tag field in the bog information section, and hit the check mark to publish. It may take some time before your image is posted to ADN. It depends on when IFTTT checks your blog for updates.
The second method involves using PourOver. PourOver is an ADN service that uses the RSS feed from your blog to publish links to your ADN stream. My WordPress blog already has an RSS feed so using PourOver involved the trivial task of authorizing to my ADN account and pasting in a link to my RSS feed. Now, every time I post content ( any content ) to my WordPress site a link is posted to ADN.