About SellerPhotoKit

Every resale marketplace wants photographs at a slightly different size, and finding out which is oddly hard. The specs are scattered across help centres, some are years out of date, and a good deal of what ranks on a search engine is simply copied from a page that was already wrong. Meanwhile the tools that will resize a batch for you mostly want an account, a subscription, or an upload of every photograph you were about to sell something with.

This site is the narrow response to that: the current specifications, a note on where each one came from, and tools that do the work in the browser tab you are already looking at.

How the numbers here are sourced

Everything on the marketplace guides comes out of a single data file, and every figure in that file carries a label saying how confident we are in it and a link to where it came from. There are two labels, and the distinction is the whole point:

First-party

Read directly off the marketplace's own help centre, seller guide or API documentation, with the link published on the guide page so you can check it yourself. Most of the numbers on this site are of this kind.

Derived

The marketplace does not publish the figure at all, and what you are reading is a conservative reading of secondary sources. 3 of the six marketplaces here do not publish pixel dimensions — Depop, Vinted, Mercari — and rather than quote a confident-looking number anyway, those pages say so on their face.

Where sources disagree, we take the more conservative figure. If one page says a listing takes twenty photographs and another says twelve, the guide teaches twelve, because a seller who prepares twelve photos for a twenty-photo cap has lost nothing and a seller who does the reverse has wasted an evening. The same rule applies to file size limits and photo counts.

Each guide also carries the date its specs were last checked. That date is not decoration — Poshmark changed its cover photo shape in March 2026 and a great many published guides still quote the old one, which is exactly what a verification date is for.

Why the tools run on your device

Resizing, compressing, stripping metadata and whitening a backdrop are all arithmetic on a grid of pixels, and every browser released in the last several years can do that arithmetic locally. There is no technical reason to send a photograph to a server to have it made smaller.

So we don't. There is no upload, no account, no queue and no copy of your photographs anywhere but on your own machine — which also means a batch of thirty large files is fine, because nothing is waiting behind anyone else's batch. You can confirm all of this rather than take our word for it: open your browser's network inspector, run a batch through, and watch nothing leave.

The privacy policy says the same thing in more detail, including the one piece of data this site itself stores on your device — which colour theme you picked — and what the adverts and the traffic counter store, which is the rest of the list.

Why it is free

The site is static files on a content delivery network. Because nothing is processed on a server, serving a visitor who resizes two hundred photographs costs no more than serving one who reads a page and leaves — which is the reason a tool like this can be free permanently rather than free until the bill arrives.

Running costs are covered by advertising, placed below the tools rather than around them. There is no paid tier, no export limit, no watermark on the output and no account to make. If the day comes that this cannot be sustained, the honest thing is to say so on this page — not to quietly move features behind a login.

The adverts are Google's, and they are kept at arm's length from the tools: the ad code sits in the page and has no access to your files, your filenames or your results. Everybody is shown adverts, including people who decline the personalised kind — declining changes how an advert is chosen, not whether the site works. The privacy policy sets out exactly what is stored on your device in each case, and what the two traffic counters do and do not record.

What this site will not do

• Ask you to sign in. There is no account system to sign in to, which is also why there is no password to leak.
• Upload your photographs. Not for processing, not for “improving the service”, not for training anything.
• Tell you a number we are not sure about. A marketplace that publishes no file size limit gets “not published” on its guide page, not a plausible-sounding invention.
• Recommend a tool that would get your listing removed. Vinted prohibits image editing outright, so the Vinted guide says as much and does not link the background whitener. We would rather lose the click.

The tools, and who each is for

Etsy is what these guides call a High detail marketplace: buyers zoom into the weave, and the platform asks for large dimensions inside a small file. Poshmark is a Mobile feed one, where the shape of the frame decides far more than the pixel count does. The tools are built around that difference rather than around a single “correct” export:

• The batch resizer crops or pads a whole folder of photographs to a marketplace's frame and hands them back as a ZIP.
• The EXIF remover deletes the GPS coordinates your phone wrote into the file. If you photograph items at home, this is the one on this list that matters most.
• The compressor searches for the highest quality that fits under a file size you name, which is what Etsy's one-megabyte limit actually requires.
• The DPI checker answers whether an image is large enough to print at a given size, for anyone selling art or prints.
• The background whitener lifts an almost-white backdrop to white. It is honest about what it cannot do, and it will tell you when your background was never plain enough.

Found something wrong?

Marketplace specifications change without announcement, and the failure mode of a site like this is a confidently wrong number sitting there for a year. If a figure here does not match what you are seeing in the app, that is the most useful message we can receive — tell us at [email protected], ideally with a link or a screenshot, and the data file and the verification date both get corrected. The contact page has more on what to include.