ChatGPT with vision (GPT-4o and GPT-4 Turbo) can analyze images attached to your conversation, but the number of images per message has practical limits depending on your plan and the interface you're using. More critically, even when multiple images are accepted, they are separate inputs: nothing in the files ties one to the other, so the wording of your prompt has to carry the relationships.

By merging images into a grid before uploading, you send one file instead of several. Instead of asking ChatGPT to 'compare image 1 and image 2', you upload a single image with both panels side by side and ask it to analyze the differences: one image, one layout, with the differences right next to each other instead of split across two files.

Practical scenarios: (1) before-after comparison: merge before/after photos and ask ChatGPT to quantify the visible differences; (2) product comparison: merge 4 competitor product screenshots and ask GPT to compare features; (3) UI review: merge 4 app screens and ask for UX feedback across the full flow; (4) chart analysis: merge 4 analytics charts and ask for trend identification across all metrics simultaneously.

The grid approach works across all GPT-4 vision-enabled interfaces: ChatGPT web, the API, and third-party tools that support vision.