I run a small free tool called imgi. You drop in two images, drag a slider to compare them, and get a permanent link to paste anywhere. Before and after shots, mostly: a photo edit against the untouched shot, a game mod next to vanilla, an AI upscale against the source file.
Here's what nobody warns you about when you build one of these. The hard part isn't the slider. It's the bandwidth bill.
Every viewer who opens a comparison pulls down two full-resolution images. One link that catches on, a few thousand views, and you're pushing gigabytes out the door. On most cloud storage the egress is what gets you. AWS S3 charges about $0.09 per GB to send data out, and storage itself runs around $0.023/GB a month, so holding onto the file is cheap and handing it to people over and over is where the meter actually runs.
Run the numbers on something that's supposed to be free and shareable. A single before/after pair might be 8MB. Ten thousand views is 80GB leaving the building, call it seven bucks for one link. Feels like nothing until a few comparisons actually spread and you're looking at hundreds of them. That's the quiet reason a lot of free image tools bolt on limits, or drown the page in ads, or just disappear one morning after the founder finally does the math. imgsli, the before/after tool a ton of people leaned on for years, went offline a while back. I don't know their reasons and I won't invent them. But I recognize the shape of the problem, because I stared at the same spreadsheet before I wrote a line of code.
