The cover picture must meet strict resolution requirements: it must be 270 x 165 pixels.
If your photo does not match this format, you will need to resize it and possibly crop it.
If your photo is the correct size but it is still not being accepted, please ensure that it is in a JPEG or JPG format and that it does not exceed 4MB.
If you need to change the cover picture, just go onto the exhibition page by clicking on the pencil icon. Then click on the cross on the top right of the existing image to be able to add a new one, click on the "+" and pick the picture you want.