Compatibility

The Photo Feed Display should, in theory, work with any well-formed RSS or Atom photo feed. For basic feed parsing, this projet makes use of SimplePie, a wonderfully simple PHP class.

Below are some services for which successful feed display has been verified:

YouTube
Flickr
Instagram*4
Pinterest*5
Picasa*
500px
imgur
Vine (via seenive.com)
ZenPhoto*2
Gallery (2/3)
Plogger
SmugMug
Tumblr.*3

Let us know if you find another (preferrably, widely used) service for which Photo Feed Display works, or, more importantly, does not work, and we will try to address it promptly!

Issues

Thumbnail duplication may occur under the following circumstances: Items contain similar (or, no) title AND photo date/time properties are not properly set. This is because file naming is determined as follows: [date/time]_[title]_[thumbsize]px.jpg. This should make each unique, as long as titles are set and/or date-time properties are correct for the photo. If not, manage your photos better. Or at least give them unique names. Sheesh!
(UPDATED 2011-01-24)* Picasa Issues | Large Picasa feeds error out due to a problem with PHP versions prior to 5.3. While I don't like this, it is kinda reasonable since RSS feeds should be small. Luckily, there is an easy work around: Google was nice enough to give us an option to append to their RSS reeds to delimit the number of results (add &max-item=10 to the end of your feed). Be sure to URL-encode it!
(UPDATED 2011-01-24)*2 ZenPhoto Issues | When using Album RSS, (1)I sometimes get blank thumbnails, and (2)occasionally thumbnails from other albums. This seems to be caused by two different issues:
1. (1) ZenPhoto seems to create the RSS feed on demand, as opposed to ahead of time. Our code is often faster than the ZP RSS generator (since it has to create thumbs and all that jazz); hence we don't find the RSS when we go looking for it. The good news is that you can fix it. Just reload the page with the PFD widget option &alwayscreatethumbs=true at the end of your feed to recreate the thumbs. Hopefully they aren't blank, now.
2. (2) This seems to be due to the way we at PFD handle RSS Feed Titles; we use them as unique album identifiers and ZenPhoto uses the Site Title + Folder Name as the feed title. If Folders (or Subfolders, in my case) are named the same thing, a non unique feed title is used for the RSS feed occurs, something which must be unique for the Photo Feed Display widget to work properly. In addition to URL-encoding your feed address[1], I also had to manually edit my rss.php file in my zen photo implementation. Hopefully, you won't have to do this. Let me know if you need help.
3. (3) The recent update relegated some accommodations I had made for ZenPhoto since it is far from the most used type of RSS. I realized that isn't fair, since ZenPhoto was the reason I created this to start with...so I made a fix. If your ZenPhoto feed is showing blank (black) thumbnails and the fixes above don't apply, try adding the following to the end of your feed (after you've used the widget builder to get everything else looking how it should): &oldpfd=true -- hope that helps!
(UPDATED 2013-08-04)**3 Because Tumblr feeds (and any other feeds that don't always include pictures) don't always include pictures, a default image is displayed for non image posts.
*4 Instagram doesn't seem to offer rss feeds by web directly, so I had to use INK361 (and give it permission) to view a RSS feed. There may be an easier way.
*5 I used this link to determine how to get a Pinterest RSS Feed. Didn't seem obvious from a glance at the website.