Before you say "Flameshot", please give me a chance to explain!
On my Mac, I use a tool called Shottr, which is great, not only can I take a screenshot and then proceed to annotate it, I can also load in an image that does not come from taking a screenshot (like an image downloaded from the internet, or a picture taken by my phone) and annotate that as well by directly opening the image with Shottr.
I just tried to do this using pictures I took with my phone that had content I wanted to pixelate, so I grabbed Obfuscate (the GNOME app), and it loaded the images turned sideways and I couldn't rotate them back, and it also only had blackout and a mild blur which didn't really cover anything up.
I installed Flameshot, but I don't seem to be able to open an image with the Flameshot editor (doesn't show up with the Open With dialog, and I didn't feel like having to open the file via cli was a good solution). I gave up and ended up just using my Mac to quickly pixelate what I needed.
On KDE, I think Spectacle was able to do this just fine, but I'm trying the all-GTK all-GNOME approach and don't want to pull in a bunch of dependencies just to get Spectacle.
Here's an example of what I'm able to do with Shottr and why I prefer its tools...I can blur, I can blur only text (it can somehow detect this, I can even erase only text as well:
And I'm able to do that very, very quickly. I realize tools like Kirta and GIMP could achieve something similar, but Shottr takes seconds to open, edit, and copy to clipboard.
Any suggestions on tools?
I wish ShareX had a Linux version. I use it at work on Windows and it’s able to edit other pictures within the app like what you’re looking for.
You might try going to AlternativeTo, filtering by apps available on Linux and trying a few. On Linux my favorite is definitely Flameshot, but you might find something closer to ShareX.
EDIT: Here’s the alternatives page for Shottr as well.