If you are not very familiar with image sizes and resolution, here is a little help.
Here at Holistic Events Australia are offering a beautiful platform to showcase your event. Hence we would like to you upload your image in LANDSCAPE format, meaning the width of the image is bigger than the height.
Resolution plays a big factor, basically we could accept large images but we do resize them while they upload, so the way the image looks like could be very different. Therefore we advise you to scale your image to a max. of 800 pixels width and 500 pixels (or less) height.
The best format to use is .jpg or .jpeg. This will make sure that all the background is covered (no transparent areas).
If you are not familiar with resizing images, please go to http://webresizer.com and this will allow you to resize your huge images simply by defining scale image % or by defining length of pixels.