It seems that when I upload an observation from my computer, and then crop a picture with the mobile phone application, there is a loss of resolution for this image.
I don’t have this problem when I upload images with my phone…
I don’t quite understand the methods you’re describing, but I would suggest looking into scaling the image instead of cropping the photo. When you take a picture of something, it has a certain amount of megapixels associated with in (more = high quality). When you crop a photo, you’re magnifying a smaller frame of the original picture in question, so you’re losing the peripheral megapixels, causing a reduction in quality. If you, however, scale the image in software (ie: GIMP), you can lower the overall size of the picture, while keeping quality high (GIMP sets it to maintain 80% quality upon scaling down, but you can toggle it up to 100% retention).
Make sure you have the latest version of the iNaturalist app installed on your phone. You could also try using a different device or browser for uploading images. And try uploading the image in its original resolution without cropping it, then if you want to crop go back in and do an edit on the picture.
This smaller image is what gets stored on iNat’s servers
The problem comes when you try to crop the image on your phone.
If you uploaded on the site, your phone will download the smaller, scaled version from iNat’s servers and crop that image.
But if you uploaded from your phone, the app still has access to the original, unscaled photo that you took and crops that. Hence the difference in quality
I’ve just done some testing, and it appears that the photo cropped via the mobile app still gets scaled down more than you would think it should be.
I uploaded a 4000x3000 photo via the website. It got scaled down to 2048x1530(or something). Then I downloaded the scaled version of it on my PC, cropped a part of it and got an image of around 700x700. Then I went and cropped the image in the mobile app to around the same area and applied changes to the observation. After the photo got updated, I downloaded it on my PC, and then it turned out it’s around 350x350…
iNat does offer different size version of photos for downloading. It’s possible that on mobile it is downloading one of these smaller versions to start out with. I would check that the size of the downloaded image on mobile (prior to cropping) is the same size as you are getting on desktop.