You may use the GIMP as a free download (you can get it link) in order to create your images. It's what many of us use.
The banner images need to be 800x100 pixels at a minimum in order to avoid zooming. Anything smaller will be resized to fit those dimensions. Anything larger is, too, so you should always use that aspect ratio (8:1)...for instance, you could have a higher-resolution image at 1600x200 pixels.
Note that GIMP tells you the dimensions of any image you view or select using the selection tool (as will any good image manipulation program, such as Photoshop).
The banner images need to be 800x100 pixels at a minimum in order to avoid zooming. Anything smaller will be resized to fit those dimensions. Anything larger is, too, so you should always use that aspect ratio (8:1)...for instance, you could have a higher-resolution image at 1600x200 pixels.
Note that GIMP tells you the dimensions of any image you view or select using the selection tool (as will any good image manipulation program, such as Photoshop).
