So me and my buddies host a Runescape Private Server for fun. Our main goal is to completely redesign the Login Screen when you first double click the .java application to load the game. We are wanting to put a sort of gif or animation of little particles just floating across the background like little lightening bugs on the Login screen. We want it to continuously loop seamlessly. We cant, however, decide if a gif is even possible to loop in the background or if it should be multiple photos stitched together to make a sort of "loop". Can we get some feedback from you guys please? I hope i explained it well enough lol. 

Any animation is just a sequence of slightly different images. They just change too fast for your brain so you see movement. Note this also includes television, and movies on mobile. Looping is indeed making the first and the last image also "slightly different" so your brain doesn't see a jump.

How you make the images appear is entirely up to you. You can repeatedly display a different picture. Do it fast enough and you get an animation. If the display framework supports it, showing a file containing an animation will work too (the display framework then displays the different pictures instead of you).

For all the details on animated gif, wikipedia is a good source: https://en.wikipedia.org/wiki/GIF#Animated_GIF

Thanks for the quick reply. I really appreciate it.

I didn't take a look into the capabillities of private Runescape Servers. What features do you have to display a background? Just a single image? Multiple images? Multiple images with variable size? Multiple images that can be adjusted on the fly (e. g. moved around, scaled, ...)? Video playback?

You'll most likely be unable to just include a gif file. If the game supports gifs, it probably will only read the first image. If you're able to display multiple images, or you're at least able to update the image(s) at runtime, you could still achieve what you want.