What photo does the UK ETA need?
A digital picture of the traveller’s face, which you upload on the GOV.UK form or take inside the UK ETA app. GOV.UK sends ETA applicants to its rules for digital face photos: a JPG of at least 600 by 750 pixels, from 50 KB to 6 MB, unedited and not mirrored.
A photo that misses the rules can delay or sink the application, so check it before you submit.
