There is a method I use and is quite simple. Create your informer and display only 1 entry.
Make sure it's ordered so it displays the newest photo or entry and under Additional Options, type in the EntryID of the photo you want to be displayed.
This is where administrator powers come in. You can find the EntryID in a variety of ways:
1. View an entry, and click Design tab on the userbar and go down to List of Page Variables, find phEnt# - you only need the number.
2. Go to Entries Management in the control panel for Photo Albums, the entry ID's should be listed on the left of each image. Just find the corresponding image or the image you want to be displayed.
It isn't as tedious as you'd expect because after all, you are the one choosing the image of the day. All you have to do is find the ID and edit your informer each day for the correct ID. Be aware that informers take a little time to change, but it shouldn't be a problem.
There is another way which is much easier to choose the image, but it's not very intuitive. You would have to use a custom field and adjust your template so regular users can't accidentally choose the option.