To explore the humor or irony in this sentence, one must first understand what the sentence is conveying. The speaker is describing the content of an image provided by someone else, presumably with the intent of discerning some text within it. However, the image doesn't contain any visible text. It merely displays a pair of cyclists, donned in Victorian or Edwardian clothing, each riding distinct types of bicycles. The irony here might arise from the expectation of text to be present and the actual absence of it.
The time period referenced within the image also adds a layer of irony. The late 19th to early 20th century was a time when the written word was instrumental in sharing information; telegrams, newspapers, and handwritten letters were dominant modes of communication. The mismatch between the image’s period setting and its lack of textual information can be seen as mildly ironic, since an absence of text in this historical context would be relatively unexpected.
The sense of humor or irony may also come from the contrast between the simplicity of the picture and the complexity or importance that may have been implied by requesting analysis of the image. One could imagine that the original submitter of the image sought out the speaker's expertise, likely expecting some detailed, text-based communication to analyze. The speaker's response straightforwardly stating that the image is merely a photograph of two people on bicycles therefore somewhat undermines the expected importance of the task.
Further irony could be found in the picture's content itself - the situation of a man on a penny-farthing (a type of bicycle with an abnormally large front wheel) and a woman on a traditional bicycle. The man is riding an outdated, arguably impractical bicycle, while the woman is on a more modern, easier-to-use bicycle. This reversal of assumed gender roles, especially considering the time period of the attire, likely would have been unexpected and is, therefore, ironic.
Humor in this scenario could stem from the mental image evoked. The picture of a man on a penny-farthing (which is inherently a somewhat comical mode of transportation due to its disproportionate wheel sizes) and a woman in late 19th-century attire on a traditional bicycle is somewhat amusing. This, combined with the anticlimax of expecting to find crucial textual information in the image and finding just straightforward content can create an element of absurdity.
Lastly, there is an element of deadpan or straight-faced humor in the speaker's description, often affiliated with British humor. This type of humor is derived from how seriously the speaker delivers a plainly absurd or even ridiculous statement. So, in the face of an escalation of seriousness, the audacious anticlimax of the expected textual discovery becomes a funny narrative note. In essence, the buildup and subsequent letdown provides the audience with a sense of amusement. The image you've provided does not contain any visible text. It shows a sepia-tone photograph of a man on a penny-farthing bicycle and a woman on a traditional bicycle, both dressed in what appears to be early 20th century or late 19th century attire.