Hello! Hope you are well! Do you need an special size for the images?

Thank you

No, there is no special size as I am hoping to be able to use the image in a range of places e.g. a website slider, in app stores, etc. I am looking to convey the concept of lots of people coming to an agreement using my app named consensus but I don''t want a picture of lots of people looking at mobile deices .... I am looking for a before and after image i.e. before "people are not in agreement" but after using the app "people are in agreement and progress is occurring"