What is the best solution/API for this? On my site users upload image, tag then and more. Instead of displaying the normal page where it shows the image and info (date, desc, user comments, etc) I want it to go to the next/prev image. Preferably with preloading. This code could be done either in flash or javascript, but I would need a way to give the user a link so they can pass it to someone else to continue at the same point.
Another thing I would like to support is a 'gallery' mode where it displays thumbs of multiple images and allows scrolling through them.
Is there an API I should use or should I hand-roll gallery and slideshow code?
How about Gallery - gallery.menalto.com? Version 3 has only just been released, but version 2.3 is very stable and has an extensive API.
To do what you're after have a look at
http://gallery.menalto.com/apidoc/ItemAdd/UserInterface/ItemAddFromServer.html
for saving images from the server, and at
http://gallery.menalto.com/node/66940
http://codex.gallery2.org/Gallery2:GalleryEmbed:getImageBlock
for extracting it out again (although use "getBlock" rather than "getImageBlock")