Geograph - photograph every grid square

All images shown on the general photo pages fit within a 1024pixel-square area. If they are bigger than that when uploaded, the site software will reduce them to fit into that frame. If they are smaller than 640px, the moderator is likely to request a larger version.

Optionally, you can upload a larger version of the same photo and license that larger version with the same Creative Commons licence (unlimited free re-use by anyone for any purpose as long as credit is given) as the main image. To do this, select the largest image size that you are happy to contribute when prompted by the submission dialogue after uploading your photo in step 1. Geograph will produce the standard 1024px image as well as this higher-resolution one according to your request.

Site users can access these larger images by clicking on 'more sizes' above the main photo on the photo page.

You can upload images of any dimensions, portrait or landscape, but the file size needs to be under 8 megabytes. We do resize them so their longest dimension is 640 pixels on the main photo page. Optionally, you can also release larger versions of various sizes for downloading and re-use.
http://www.geograph.org.uk/article/Larger-Uploads-Information

We only accept JPEG encoded images. If you have any image in another format it will need to be converted.

Ideally images shouldn't have a longest dimension of fewer than 480 pixels. While we might accept such images if they hold particular interest, we would really prefer a larger image.

We do record the EXIF headers from your original image, so it is advantageous to upload your original camera image or use image editing software that maintains the EXIF data if you want this information to be kept (but we don't currently make use of the data).

The simplest method is to overwrite the large version with a smaller one.
This only needs to be one pixel larger than the displayed image (641 pixels on longest side) but can be whatever size you are comfortable to licence for reuse.
Just click on the link [Upload another large version] and follow the steps on the page.

This process works best on unmoderated images as these will not yet have been picked up by others (wikimedia, British library, site visitors etc). We cannot guarantee that images overwritten after moderation will not have been copied elsewhere before being replaced.