10. A method, comprising: receiving, via at least one network, a first communication from a device; identifying, from the first communication, a request to access a web resource; generating an image comprising pixel values in a plurality of channels including a transparency channel, the generating comprising encoding a challenge text in the image at least in part by: generating decoding information for displaying the challenge text, the decoding information including a plurality of saturation values for a respective plurality of pixels in the image; and storing the decoding information, including the plurality of saturation values, in the transparency channel of the image; transmitting, to the device and via the at least one network, the generated image and software code that, when executed by the device, uses the decoding information to facilitate displaying of the challenge text by the device; receiving, via the at least one network, a second communication from the device; identifying, from the second communication, a response text; and providing the device with access to the web resource based on a comparison between the challenge text and the response text.
10. A method, comprising: receiving, via at least one network, a first communication from a device; identifying, from the first communication, a request to access a web resource; generating an image comprising pixel values in a plurality of channels including a transparency channel, the generating comprising encoding a challenge text in the image at least in part by: generating decoding information for displaying the challenge text, the decoding information including a plurality of saturation values for a respective plurality of pixels in the image; and storing the decoding information, including the plurality of saturation values, in the transparency channel of the image; transmitting, to the device and via the at least one network, the generated image and software code that, when executed by the device, uses the decoding information to facilitate displaying of the challenge text by the device; receiving, via the at least one network, a second communication from the device; identifying, from the second communication, a response text; and providing the device with access to the web resource based on a comparison between the challenge text and the response text. 12. The method of claim 10 , wherein the software code, when executed by an Internet browser, uses the decoding information to cause a plurality of graphical elements to be displayed in a webpage so that the webpage displays the challenge text.