I've made some research and couldn't find the answer. Is it possible to detect an image resolution using an upload file field?
Right now, I can detect the size of an image in pixels...But I would need it to find the "inches" size.
And I also need to find out the resolution of the image.
Using Javascript would be the best...if possible, if not...PHP maybe?
Thanks!
You'll have to do this once it has been submitted. Check out the getimagesize function in PHP - http://php.net/manual/en/function.getimagesize.php
You will need a browser that supports the FileReader interface - read more at Is it possible to get info from a file on the client side without uploading the file?.
There are some javascript libraries reading such information like EXIF from the file:
JsJpegMeta
ImageInfo - although I'm not sure whether it gets its binary data by ajax from already uploaded files.
If you want to offer this functionality to user with browsers not supporting this, you will need to upload the file and do it serverside (with PHP).
Related
While I was looking for some info, I came across this image on a forum which i didn't understood how it worked. Its a JPG image which actually tells you your ip address and your browser. I think that maybe it was made by modifying htacess and replacing PHP for JPG, and with PHP generating the image dynamically but I'm not sure about it.
Would this be the way that this works?
Here is the image i saw:
http://www.danasoft.com/sig/475388.jpg
Thanks
It is nothing but etching text on image. There are several options to do it. Using PHP see here and Java see here
yes this image is generating dynamically. It collects your info make a string and use some library to generate that image like in Captcha. php has its own library too for this purpose
Click here
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How to check file types of uploaded files in PHP?
Creating a text file and rename it to anything.jpg and try uploading it on facebook, facebook detects that the file is not an image and says Please select an image file or something like that. How do they do it?
I tested it out on my localhost by creating a dummy html form along with a <input type="file"... element and uploaded an image file created by renaming a text file to something.jpg and the file type in $_FILES['control_name']['type'] showed image/jpeg... How do I block users from uploading such 'fake' images. I think restriction using $_FILES['control_name']['type'] is not a solution, right?
When you process image on server, use image manipulation library (getimagesize for example) to detect it's width and height. When this fails, reject the image. You will probably do it anyway to generate thumbnail, so it is like one extra if.
There are many ways of checking the actual files. How Facebook does it, only the ones who created it know i think :).
Most likely they will look at the first bytes in the file. All files have certain bytes describing what they truely are. For this however you need loads of time/money creating a database or such against which you can validate the uploads.
More common solutions are;
FORM attribute
In a lot of browsers, of course excluding Internet Explorer, you can set an accept attribute which checks on extensions client side. More info here: File input 'accept' attribute - is it useful?
Extension
This is not realy secure, for a script can be saved with an image extension
Read file MIME TYPE
This is a solution like you stated in your question. This however is also easy to bypass and relies on the up-to-date status of your server.
Processing the image
The most reliable (for most developer skills and available time) would be to process the image as a test.
Put it in a library like GD or Imagic. They will raise errors when an image is not realy an image. This however will require you to keep that software up to date.
In short, there is not a 100% guarantee to catch this without spending tons of hours. Even then you only get 99,9%. You should weigh your available time against the above options and choose which best suits you. As best practice i recommend a combination of all 3.
This topic is also discussed in Security: How to validate image file uploads?
Headers in your file won't be the same.
Is it possible to upload a specific part of the file rather than the whole file? Say, I want to upload only first 100 bytes of the file, or the rest of the file given offset 100 bytes?
In more modern browsers, with the right permissions, yes. You need the browser to support file stream reading. A tutorial is here: http://www.html5rocks.com/en/tutorials/file/dndfiles/
Open the file, find the chunk you want and the POST through AJAX (e.g. with jQuery).
You may find it easier to synchronously upload in chunks and piece together serverside (e.g. with a session) - this way you can give feedback on the upload progress.
Not sure of a method for older browsers, or ones where this is blocked by the user - so you're probably better uploading the entire file (using a FILE post) and stripping out the bit you need serverside. More upload, but better support for everyone.
Edit - someone else just posted a question about this: https://github.com/blueimp/jQuery-File-Upload - it doesn't appear to support it natively, but it may also do what you want with some fiddling? You'll still need to handle the fallback, though.
Yes, it is possible. You can use javascript FileApi with BlobApi to upload any part of file. Note, this is a HTML5 feature.
If you want to investigate this features you can look at jQuery File Upload Plugin
You can use slice method of file api to get half file.
var midpt=Math.round(file.size/2);
var halfFile=file.slice(0,midpt); //specify start and end positions
I'm creating a web app that allows users to specify an image url to display an image along with their submission.
To avoid some potentially large images and odd sizes, i'd like to use PHP to limit/resize the image before it gets output to the browser (I know i could use max-width in CSS but this is unnecessary downloading)
Is this possible?
PHP has a library named GD. It's fairly easy to check the size of an image with the getimagesize() function.
You can find the complete code for it with 2 module/extensions: http://www.fliquidstudios.com/2009/05/07/resizing-images-in-php-with-gd-and-imagick/
a comparison of them can be found here: http://dreamfall.blogspot.com/2008/02/php-benchmarks-gd-vs-imagemagick.html which may be of use if you want optimize features.
On my site I have given an option to user to choose thier profile image
Type link of an image
Image is a url link, and first I want it to resize to 400x300 (image's original size doesn't matter), and then display it on my web page.
Something like below:
<img src="http://mywebsite.com/resize.php?image=http://someotherurl.com/upload/image2.jpg&width=400&height=300" />
anyone knows this kind of script, please tell me how to solve this issue.
Thanks
A recent post:
https://stackoverflow.com/questions/1302464/php-image-resize-my-upload-script
has some code and comments that may give you some pointers. Otherwise may I suggest
http://www.white-hat-web-design.co.uk/articles/php-image-resizing.php.
Good luck!
If you have the GD extenstion, you can use imagecopyresampled (the documentation also features some examples). However, if the image to be resized is large and there is a low memory limit on your server, you may run out of memory.
I don't have ready to use source code, but it should look like:
Load image pointed by image parameter into object of ImageMagick (or other graphics library).
Resize it.
Send content to output stream.
Optionally you could:
Check if loaded file is image (plus other validation checks).
Save resized image on disk and serve it from disk next time (if you do it often).
Check docs of you favorite graphics library used in PHP for details.
Good luck!
Use the Class called - class.upload.php.
Find it at: PHP Classes
We use it at all times in many of our work.
The name is deceptive but actually it is an uploader as well as image processor. It has a very big list of functionality for resizing images, adding text to images, converting formats, etc. etc.
There is sample code which shows how to read an Image from server, modify it and finally send it directly to browser without having to create a temp file on server.
HTH