[PERSONAL OPINION OF THE AUTHOR] Geograph takes pride in taking care about accuracy of location and information content. We like to think that this sets us apart from many other picture sites on the internet.
Whether it is one of your own pictures or someone else's, if you think something's wrong, please use the 'change image details' or 'suggest update' link under the main picture. This gives you access to a form where you can amend any of the details (subject and camera position, view direction, title, description etc). After making your changes, leave a short explanation in the box at the end of the form.
Changes to your own images will update immediately. The only exception are changes to the subject grid square, which are moderated; this will typically take a day or so.
If you suggest changes to someone else's pictures, they will be alerted and have an opportunity to reply. Ideally, you should work with the original contributor to come to a consensus. Moderators will try to assist with that. Generally, accuracy is taken very seriously, but if additional information is presented, it is the photo contributor's prerogative to decide whether to accept it.
When making a suggestion, please bear in mind that you are communicating with the original author, not primarily with Geograph. Explain your changes in a friendly and civil manner, and supply sources to verify your point. Avoid making many suggestions to the same contributor at the same time.
Suggestions which are mainly concerned with geograph/supplemental classification or seek to move positions by small amounts within the stated precision (often 100m) are regarded as a waste of time by many and can cause aggravation out of proportion with their usefulness.
Once you have pressed the "I agree" button your picture is in the system and subject to the Creative Commons Licence.
If the picture has not yet been moderated, you can requested for the image to be rejected, and you will be asked to give a reason. To "self moderate" in this way you click on the "Change Image Details" link under the picture: you should see an icon for "reject".
Once the picture has been moderated and accepted you will probably need to give a very good reason for the image to be removed from display. Images may be removed from display if they were taken illegally, or, for example if a landowner objects to a picture taken from a place without public access. This process of removing from display is sometimes referred to as "vaulting" as a copy of the picture remains in the "vault": a file storage area.
Actually I like Photoshop. It IS expensive, but you can purchase cheaper versions of it which are perfectly capable. It does take a little time to learn, but if you can master the keyboard shortcuts it helps a lot. It really can do everything - from HDR to 3d painting.
There are loads of Image editing applications, including the free one GIMP. Its personal preference. GIMP is very capable, but I'm not personally keen on the interface, even if it is a bit like Photoshop. It also runs on Linux.
In wondows, its useful to have the application set up so that a right click on the image will launch the application, or open the image in it.
Sometimes pictures get relocated if they have been uploaded to the wrong grid square by mistake. This is often the case with images from the very early days of Geograph, when there was no or only scanned out-of-copyright mapping available.
Very occasionally, a (first) Geograph gets reclassified as a supplemental image if there had been a clear error in the original classification.
Also rarely, images are withdrawn or vaulted for a long period because they weren't taken from a place with public access and the land owner has complained.
In all these cases, the next uploaded geograph (if any) will take the point, and if that was yours, then you'll find a miraculous extra point on your profile.