A worked example
Forty phone photos, a mix of 4032 × 3024 and 3024 × 4032, with a 1600 px long-edge rule: the landscape ones become 1600 × 1200, the portrait ones 1200 × 1600, and the preflight says how many of each before anything runs. The ZIP names each file after its original with the new size added.
When another page here fits better
For one picture with a precise box and a crop you want to choose by eye, use the resizer on the front page. For a set of sizes from one picture, open the Sizes panel there.
What stays on your device
The whole folder is decoded, resized and zipped in this tab. File names stay in the page, and nothing — not a picture, not a name, not a count — is sent anywhere.
A large batch is limited by the device's memory, not by a server. If a phone struggles, run the folder in two halves.
Questions people ask here
How many pictures can I resize at once?
There is no fixed cap. The page runs one to three files at a time depending on the device, releases each picture as soon as it is written, and adds it to a ZIP built in this tab.
What happens to portrait photos with a 1920 × 1080 box?
With “Turn the box for portrait pictures” on, they get 1080 × 1920 instead, so they are not letterboxed into a landscape box. Long and short edge rules handle orientation by themselves.
Can every file be kept under a size?
Yes. Set a file-size limit in the Output section; each JPG or WebP is searched for the best quality under it, and any file that cannot get there is marked in the list.