You take a photo, you try to upload it, and the form refuses. The message is usually short and not very helpful. Almost always it is one of two problems, and they need opposite solutions.
A form can be strict about two completely different things.
The file size is how much space the picture takes up. It is measured in KB or MB. A form might say "maximum 200 KB". This is about the weight of the file, not how it looks.
The pixel size is how wide and tall the picture is. A form might say "600 x 600 pixels". This is about the shape and detail, not the weight.
The confusing part is that both problems produce the same words on screen: too big. So the first thing to do is read the message again and look for the unit. KB or MB means file size. Pixels, px, or two numbers with an x between them means pixel size.
This is the common one. Phone cameras have got very good, and a normal photo today is often 4 to 8 MB. A form asking for 200 KB wants something about thirty times lighter.
The fix is compression. That means the picture is saved again with less data in it. The width and height stay exactly the same, so it still fits the same box on the form — it just weighs less. Fine detail gets softer, which nobody notices on a photo of a document or a passport picture.
Use the Image Compressor. Type the number the form asked for, and it works its way down until it lands under that limit.
Here compression will not help you at all. You could squeeze the file to 30 KB and the form would still say no, because it is measuring width and height.
What you need is resizing. Use the Image Resizer and type the exact numbers the form asked for.
One thing to watch: if you make a photo bigger than it was, it will look soft and blurry. Detail that was never in the picture cannot be added back. Going smaller is always safe. So if a form wants 600 x 600 and your photo is 4000 x 3000, you are fine. If your photo is 200 x 150, take a new one.
Passport and visa forms are the strict ones. They often want an exact pixel size, an exact shape, and a file under a certain number of KB, all at once.
Do it in this order, because doing it the other way round wastes the work:
If you compress first and then resize, the resizing throws away the compression work and you have to do it again.
For passport and visa pictures the Passport Photo maker does the cropping and sizing in one step, with the common sizes already set up.
Before you start, write down exactly what the form asked for. Not roughly — exactly. The number, the unit, and the format.
Most of the time people lose an evening to this because they are working from memory: they think the limit was 100 KB when it was 100 MB, or they resize to 600 x 800 when the form wanted 600 x 600. The tools are fast. Guessing is what takes the time.
The photos people have to shrink are usually not holiday snaps. They are passport pictures, ID cards, pay slips, medical letters. It is worth knowing where those files go.
Most online tools upload your file to their server, change it there, and send it back. For a while, your document sits on a company's computer. The tools on this site work differently: your browser reads the picture from your own device, changes it there, and hands it straight back. Nothing is uploaded and nothing is kept.