=== The Issue ===
I believe the issue you are experiencing is due to having images that require cropping. When an image is uploaded and it isn't in a 4:3 aspect ratio, it will appear with an orange border around it as pictured here:
=== Crop Required ===
[image|123444]
''Note: You won't be able to drag and drop the image, it would select it as if it were text.''
=== Solution ===
To fix the issue you need to crop the image by selecting the wrench icon in the top left corner of the image, cropping the image, then saving the image.
[image|123445]
The image will then be able to be dragged and dropped onto a step.
[http://www.dozuki.com/Help/Uploading_Images|More information about uploading, cropping and placing images on guides and wikis is available in the Dozuki Help Docs.]