This is how I’m hanging my photos (and other stuff) on a picture rail using a fishing line (I didn’t make this video, just found it on YouTube):
As you can see, the line shown in the video is yellow(ish) — but that’s just for demonstration reasons. It looks (hides) way better if it’s transparent. (Surprise, surprise…) And don’t forget about the weight of whatever you’re using it for: a heavy-duty (0.5 mm) fishing line can hold up to 17 kilograms; a bead thread just as thick might handle up to ten. In any case, make sure to read the description on the reel to prevent your cat from being killed by a picture frame or an ornamental welded piece of art.