Not all the pictures and film has been altered, but even if that were true, you can only alter a picture of something if...you have a picture of the something...
You need to have the image, yes...
Right. Good. And how do you get the images of the globe earth without being in space?
But all of them have been altered...
Easily demonstrable...
Just gather all of the images released by NASA of the supposed globe earth and compare them.
None of them depict the same thing.
OK. Well here's 3 pictures I took of a globe I have. I have not altered any of these images (full disclosure, I have cropped them, but that's all, I've not applied any filters). I've simply put them into one image and reduced the size of the combined image. I've not altered any of them in the way you mean, I've done nothing to change the way the images actually looked when I took them:
Those are 3 pictures of the same object. Do they look the same? The top one I stood quite close to it and took a picture.
The second one I stood further away and zoomed in.
The last one I stood further away than the first but closer than the second and I changed my camera setting, you can see the lighting looks quite different. Actually though I took the 3 pictures within a minute and all of the same object.
I've attached the picture in case you are still having that imgbb problem.
So while NASA may well alter some images to enhance them, not all of their images are altered and different pictures of the globe looking different is simply because the pictures were taken from different distances and with different cameras or settings.