Technically, downloading such pictures and sending them to others is copyright infringement, unless they have been released under a license which permits sharing them with others.
Copyright infringement is not a crime. It is a tort. That means the copyright owner can sue, if and when the owner learns this has happened, and chooses to bring a court action. As that would involve paying a lawyer, and court fees, and other expenses, most owners will not bring such a suit unless they think the damages are likely to be large enough to make it worth their time and trouble, over and above getting their expenses back. Most copyright owners would not bother to sue over personal sharing of pictures posted on the net. However, that is the choice of the owner to make, if they learn of the sharing.
Note that, if instead of attaching a picture to an email, one sends a link, there is no copyright infringement involved, even technically.
While the details of copyright laws differ in different countries, the information above is true for both the US and the EU, and most if not all other countries.
One of the ways in which copyright laws differ between countries is in the exceptions to copyright that are available. In the US there is the somewhat complex concept of "fair use". Being personal and non-commercial use does not automatically make something fair use, although it helps support a finding of fair use. Some EU countries have a specific exception for personal use. I believe that India has such an exception also. Many countries have exceptions for news reporting, use in classroom teaching, parody, and various other cases.
I said above tyht copyright infringement is not a crime. That is not always true. Under 17 USC 506 infringement can be criminal, but only if the infringement is:
- willful;
- for private financial gain or commercial advantage; and
3A) of works valued at over $1,000, or
3B) of a work being prepared for commercial distribution, knowingly preempting such distribution by electronic posting.
I believe that there are similar limits on criminal copyright infringement in the laws of other countries.
Beyond that, the current policy of the US Department of Justice is to prosecute criminal copyright infringement only when it is done on a bulk basis, as a business. In particular, mass reproduction and sale of CDs and DVDs without permission may be prosecuted.
Comments point out that a plaintiff may, in the US, elect to receive statutory damages, instead of actual damages, and in that case need not prove any financial loss. This is true, but the damages may be as low as $750 per work infringed (not per copy) or as low as $200 for "innocent infringers". The amount is set by the court, as it thinks just.
It is also true that a US court may award reasonable attorney fees and costs, under 17 USC 505. But this is wholly in the court's discretion, it is in no way automatic, and I understand is typically not awarded in "minor" cases. In any case a plaintiff cannot count on getting fees and costs, nor on a large statutory damage award.