1. A method for generating, by a processor, an image for use in a test to tell computers and humans apart comprising: receiving, by the processor, a selection of a range of characters corresponding to code points from Unicode plane 0, the selected range of characters at least including the 8-bit ASCII character range; receiving, by the processor, a selection of a font for the selected range of characters; testing, by the processor, each character in the selected range of characters, characters of the selected range of characters that pass the testing forming a challenge character subset, the testing comprising: determining if the character has a glyph in the selected font; determining if the character is a whitespace character; determining if the character leaves a visible impression; receiving, by the processor, a selection of a number of challenge characters; generating, in response to receiving a request for an image, by the processor: a challenge comprising a plurality of selected characters from the challenge character subset, the number of characters in the challenge equaling the selected number of challenge characters, and a response comprising a plurality of characters from the challenge character subset, the response having a character count that is greater than the selected number of challenge characters and the response including the characters in the challenge, each character in the response having a font size selected from a range having a predetermined maximum, the generated image comprising the generated challenge and the generated response; and calculating, by the processor, a solution threshold, the solution threshold being a value based on the selected font size of each of the characters in the challenge included in the response and a predetermined distance from the locations of each of the characters in the challenge included in the response.
1. A method for generating, by a processor, an image for use in a test to tell computers and humans apart comprising: receiving, by the processor, a selection of a range of characters corresponding to code points from Unicode plane 0, the selected range of characters at least including the 8-bit ASCII character range; receiving, by the processor, a selection of a font for the selected range of characters; testing, by the processor, each character in the selected range of characters, characters of the selected range of characters that pass the testing forming a challenge character subset, the testing comprising: determining if the character has a glyph in the selected font; determining if the character is a whitespace character; determining if the character leaves a visible impression; receiving, by the processor, a selection of a number of challenge characters; generating, in response to receiving a request for an image, by the processor: a challenge comprising a plurality of selected characters from the challenge character subset, the number of characters in the challenge equaling the selected number of challenge characters, and a response comprising a plurality of characters from the challenge character subset, the response having a character count that is greater than the selected number of challenge characters and the response including the characters in the challenge, each character in the response having a font size selected from a range having a predetermined maximum, the generated image comprising the generated challenge and the generated response; and calculating, by the processor, a solution threshold, the solution threshold being a value based on the selected font size of each of the characters in the challenge included in the response and a predetermined distance from the locations of each of the characters in the challenge included in the response. 2. The method of claim 1 , further comprising: formatting the generated image, by the processor, based on the dimensions of a display device, the formatting comprising: aligning the selected characters of the challenge horizontally and placing the selected characters of the response below the selected characters of the challenge when the display of the display device has a greater height than width; and aligning the selected characters of the challenge vertically and placing the selected characters of the response adjacent to the selected characters of the challenge when the display of the display device has a greater width than height.