Glad your dog is doing well! One of our previous Labs, Mocha, had similar surgery and got 7 more years of running from it, so it was totally worth it.
Attackpoint doesn't store photos like Facebook does, so you need to upload them somewhere else and copy the appropriate HTML code into your log entry to embed a JPG.
There are photo storage sites that make it easier. You can upload your photo, click on it and ask for "embed code" to be generated. Then you just copy and paste the HTML code into your Attackpoint log.
I used Picasa for this for years but Google has stopped support and moved to Google Photos, which doesn't have embed functionality. As I read more about this, I learned that it isn't in the best interest of a free photo storage site to let you embed photos on someone else's site. It was no mistake on Google's part; they want you to go to their site. Also, there is zero obligation on the part of a free photo storage site to keep offering their product, improving their product or offering a particular feature of their product.
So when I was looking for a different solution, I decided not to go with Flickr for that reason. I now upload photos to SmugMug, which has a fee but it's reasonable. It is used by professional photographers as well as serious amateurs. I feel more confident that it won't just disappear or remove a key feature. So far, so good! :)