When you look at a photo on say a major web site, even simple stuff like the box shot of Easy Photo Denoise on GOTD, the colors are generally solid, and with the exception of some compression artifacts, not too different than what you see with graphics like a chart or graph created from a spreadsheet, or maybe clipart. Look at a photo with noise, and those solid colors are mottled or speckled, with the image itself looking not quite sharp or in focus.
With a digital camera, including those in cell phones, light hits the sensor, and electronics turn the electrical signals from the sensor into the photos we see. It's a difficult job that even the monitors and cell phone screens we look at to view those pictures can't get 100% right. A certain amount of noise happens just because that's the best that a particular camera can do -- how much noise you get varies by make and model. In higher end cameras you can increase the ISO, which basically means turning up the sensitivity to light, so you can take pictures in dim or low light conditions. You see the same sort of thing in some cell phone cameras, where the software can collect data from the sensor for a longer period of time. When the sensor elements get hot [say because they're active longer], &/or when the ISO is increased, the amount of noise increases too.
If/when you edit your photos, it's really difficult for software to get rid of that noise, because software doesn't have your native intelligence -- it has no idea whatsoever, no hint or clue on what that picture's supposed to look like. It can't tell if somewhat isolated dark pixels are noise, or if they're part of a surface's texture. So using denoising software or plugins or FX has traditionally meant some blurring, as object edges are smoothed along with the noise in that object's [& the background's] color(s). The *hoped for* cure is to use AI [Artificial Intelligence], because it *might* be able to make a better guess at what your photo's supposed to look like.
The product page for Easy Photo Denoise 4.1 mentions AI, and it talks about uploading your photo(s), but while it does connect online [it opens four ports], it appears to be more of a standard denoising app. That doesn't mean it's terribly bad... on an old scanned photo from a print with lots of grain/noise, it performed roughly the same as Franzis Denoise projects 2 pro at its default settings. It was also close to what I got using the quick denoise in PSP 2021 Ult, but Corel's software beats Adobe to the punch, also offering AI denoise [it's something Adobe is still working on for P/Shop]. And yes, the AI did a better job, preserving more texture detail.
That said, the 32-bit only Easy Photo Denoise 4.1 installs to a single folder, with no additions to the user folders etc. And the registry gets just 2 new keys, one for uninstall & one for the app, though that 2nd had quite a few values or entries -- I recorded over 700 new registry entries in total. One nice touch is that when you get a key for the app, it's good for more than one installation, e.g. I didn't have to get a new key for each VM, 32 & 64-bit.