Aurasma can be tricky, sometimes. Our math teacher is working with it and I have worked with it as well. Sometimes your image is too complex or a bit too sparse to create a good trigger. (the following is from the website)
Trigger images should be graphically rich and not too dark or sparse.
Small text, musical notes, and other small patterns and lines will not make for good images.
Your Trigger Image is too large
Solution: Check the size of your Trigger Image. Images uploaded to the Aurasma Studio should be no larger than 500,000 pixels (height x width). You can edit the size of your image in a program like Paint or Picture Manager.
Your Trigger Image is too sparse
Solution: With this error, the Studio is letting you know that Aurasma will struggle to recognize your image because there is not enough graphical detail in it for it to pick up on and identify your image as unique. Sparse images lack graphical detail or possibly contain large gaps of blank space between more detailed parts of the image. Solutions include either using the masking tool to block Aurasma from wasting time viewing blank areas it will not recognize, or cropping the image before uploading it so as to minimize blank space and concentrate pixels around parts of the image which will be more easily identified. You may also consider using an alternative Trigger Image.
Your Trigger Image is too dark
Solution: With this error, the Studio is letting you know that the relative darkness of the image is making it more difficult for the technology to recognize the graphical features within it. You can try using the masking tool / cropping the image pre-upload to block Aurasma's view from the darkest parts of the image and focus its attention on lighter, more recognizable sections. If the image is very dark though, you may want to consider using an alternative Trigger Image.
Your Image is too complex
Solution: Here, Aurasma is finding that there is so much graphical information in the image that it is not always sure which part of the image it is looking at. This can result in a jittery, unstable launching of the Overlay on recognition of your Trigger Image as Aurasma is not sure where to place the Overlay in relation to the image. This problem is often caused by repeating patterns in an image - if the same pattern / logo / image is used in both the top-left and bottom-right corners of an image, Aurasma may not know where to place the Overlay in relation to the image as it could get the corners confused! Other images may simply have too much detail - imagine a photo of thousands of stars in the night sky or boats in the sea. Again, Aurasma may struggle to identify the image from an information overload. Use the masking tool to block Aurasma's view from these very detailed areas of an image.