You can try using a different browser maybe, or clearing the caches and cookies and disabling the add-ons of your browser in order to stave off any compatibility problems you might be facing.
However, as Tailor mentioned you should be able to do it.
Joe also said about the specific project permission, did you confirm you have it?
Under the Supported Platforms doc there's a warning about some JAVA 8 versions that are not recommended to use, are you perhaps under any of these versions?
If none of that help, please let us know if there's any information on your JIRA logs.
Feel free to raise a aupport request at Atlassian Support in the JIRA project.
Please see this thread, as I suspect this may be the same problem: https://answers.atlassian.com/questions/251286
Depending on the version of JIRA you are using, and what browser you are using, this add-on may help: https://marketplace.atlassian.com/plugins/com.atlassian.plugins.jira-html5-attach-images.
If you are using Firefox, Chrome or IE 11 and JIRA 6.0.5 - 6.2.4, you can install it. If you are using JIRA 6.2.5+, you can simply use the other browsers as this is already bundled now.
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