For those wanting an alternative to Cubbi.es that can work on any pretty much any browser here are some bookmarklets for your use. It is a modified version of the Diaspora* Share bookmarklet but this one will create a Markdown embed image for your post automatically. The icon on your Bookmark toolbar will appear identically to the standard Diaspora* Share Link so I would recommend editing it and giving it some title like "D* Image Share" to differentiate it.
Below is the list of links for each pod. Locate your pod and drag the link up to your Bookmarks toolbar.
Be sure you have ONLY the image on the browser tab you are on. You can do this by right-clicking on an image in a web page and choose "Open Image In New Tab/View Image" (or some variation on that wording).
Once you are on the browser tab with only the image on the screen, click the D* Image Share bookmarklet you created earlier and it will open up a Share window with Markdown already made to embed the image, I don't recommend modifying the Markdown code unless you understand it. You can definitely add hashtags and any other text you like below it though (unlike cubbi.es).
There is a slight aesthetic issue of a "bullet" character appearing near the image on your post. I can't change that as it pulls from the original Diaspora Sharing Page that I can't modify. If you are CAREFUL you can remove the hyphen from the beginning of the markdown text to remedy this for that post.
I do not have an account on every pod to test this bookmarklet. If it does not function though for you, unfortunately it is something specific to your pod that I won't be able to overcome.
A big thanks to Tony Baldwin for enlightening me that it is possible to use this on more than just the diasp.org pod. He has a version of this bookmarklet that include a hyperlink to the original image. It is set up for poddery.com but can be modified to your pod. His version is at http://pastebin.com/P37Y6VPQ